kernel_lock.c emits a warning because a raw spinlock function is used
with a spinlock. Convert BKL to raw_spinlock.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@elte.hu>