dca: check against empty dca_domains list before unregister provider fix

In 3.0.67, commit 7a9a20ea77e7508c795dead9ab2f6c98a617762d (dca: check
against empty dca_domains list before unregister provider), upstream
commit c419fcfd071cf34ba00f9f65282583772d2655e7, added a fail path to
unregister_dca_provider. It added there also a call to
raw_spin_unlock_irqrestore. But in 3.0, the lock is not raw, so this
results in:
drivers/dca/dca-core.c: In function 'unregister_dca_provider':
drivers/dca/dca-core.c:413: warning: passing argument 1 of '_raw_spin_unlock_irqrestore' from incompatible pointer type

Fix it by calling spin_unlock_irqrestore properly.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>