usb: musb: gadget: use pm autosuspend in musb_gadget_pullup

If musb_gadget_pullup doesn't use pm autosuspend, next may happen:

time |   pseudocode
------------------------------------------------------------
t1   | pm_runtime_put_autosuspend() scedules suspend at 't4'
     |     /* some code running */
t2   | musb_gadget_pullup: pm_runtime_get_sync() <-- cancels requested autosuspend
     |     /* some code running */
t3   | musb_gadget_pullup: pm_runtime_put() <-- suspends device (may happen before t4!)
     |
t4   | <- suspend is expected here, but device may be already suspended between t3 and t4

So use pm autosuspend in musb_gadget_pullup and prevent such situation

Change-Id: I8b9618c6d24bea3810c736f8fc0195802ce79c55
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@ti.com>
(cherry picked from commit fd5404d9033defa72dbbdaace600a67fcf9763bb)