qspinlock: use signed temporaries for cmpxchg

When building with W=2, the build log is flooded with

include/asm-generic/qrwlock.h:65:56: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qrwlock.h:92:53: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qspinlock.h:68:55: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]
include/asm-generic/qspinlock.h:82:52: warning: pointer targets in passing argument 2 of 'atomic_try_cmpxchg_acquire' differ in signedness [-Wpointer-sign]

The atomics are built on top of signed integers, but the caller
doesn't actually care. Just use signed types as well.

Fixes: 27df8968 ("locking/spinlocks: Remove an instruction from spin and write locks")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>