edac: Don't try to cancel workqueue when it's never setup

We only setup a workqueue for edac devices that use the polling
method. We still try to cancel the workqueue if an edac_device
uses the irq method though. This causes a warning from debug
objects when we remove an edac device:

WARNING: CPU: 0 PID: 56 at lib/debugobjects.c:260 debug_print_object+0x98/0xc0()
ODEBUG: assert_init not available (active state 0) object type: timer_list hint: stub_timer+0x0/0x28
Modules linked in: krait_edac(-)
CPU: 0 PID: 56 Comm: rmmod Not tainted 3.12.0-rc2-00035-g15292a0 #69
[<c02179b4>] (unwind_backtrace+0x0/0x144) from [<c0213e58>] (show_stack+0x20/0x24)
[<c0213e58>] (show_stack+0x20/0x24) from [<c06f7fc4>] (dump_stack+0x74/0xb4)
[<c06f7fc4>] (dump_stack+0x74/0xb4) from [<c0223c34>] (warn_slowpath_common+0x78/0x9c)
[<c0223c34>] (warn_slowpath_common+0x78/0x9c) from [<c0223d14>] (warn_slowpath_fmt+0x40/0x48)
[<c0223d14>] (warn_slowpath_fmt+0x40/0x48) from [<c04cf078>] (debug_print_object+0x98/0xc0)
[<c04cf078>] (debug_print_object+0x98/0xc0) from [<c04cfb54>] (debug_object_assert_init+0xdc/0xec)
[<c04cfb54>] (debug_object_assert_init+0xdc/0xec) from [<c02310c4>] (del_timer+0x24/0x7c)
[<c02310c4>] (del_timer+0x24/0x7c) from [<c023fef8>] (try_to_grab_pending+0xc0/0x1b0)
[<c023fef8>] (try_to_grab_pending+0xc0/0x1b0) from [<c0240014>] (cancel_delayed_work+0x2c/0xa0)
[<c0240014>] (cancel_delayed_work+0x2c/0xa0) from [<c059fa14>] (edac_device_workq_teardown+0x1c/0x38)
[<c059fa14>] (edac_device_workq_teardown+0x1c/0x38) from [<c059fae8>] (edac_device_del_device+0xb8/0xe4)
[<c059fae8>] (edac_device_del_device+0xb8/0xe4) from [<bf000050>] (krait_edac_remove+0x50/0x70 [krait_edac])
[<bf000050>] (krait_edac_remove+0x50/0x70 [krait_edac]) from [<c0511e34>] (platform_drv_remove+0x24/0x28)
[<c0511e34>] (platform_drv_remove+0x24/0x28) from [<c050fffc>] (__device_release_driver+0x68/0xc0)
[<c050fffc>] (__device_release_driver+0x68/0xc0) from [<c0510adc>] (driver_detach+0xc4/0xc8)
[<c0510adc>] (driver_detach+0xc4/0xc8) from [<c050fd98>] (bus_remove_driver+0xac/0x114)
[<c050fd98>] (bus_remove_driver+0xac/0x114) from [<c05111d8>] (driver_unregister+0x38/0x58)
[<c05111d8>] (driver_unregister+0x38/0x58) from [<c0511fe8>] (platform_driver_unregister+0x1c/0x20)
[<c0511fe8>] (platform_driver_unregister+0x1c/0x20) from [<bf0005c4>] (krait_edac_driver_exit+0x14/0x1c [krait_edac])
[<bf0005c4>] (krait_edac_driver_exit+0x14/0x1c [krait_edac]) from [<c028b248>] (SyS_delete_module+0x178/0x2b4)
[<c028b248>] (SyS_delete_module+0x178/0x2b4) from [<c020f760>] (ret_fast_syscall+0x0/0x48)
Fix it by skipping the workqueue teardown for such devices.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>