ARM: 8174/1: Use global stack register variable for percpu

Using global current_stack_pointer works on both clang and gcc.
current_stack_pointer is an unsigned long and needs to be cast
as a pointer to dereference.

Signed-off-by: Mark Charlebois <[e-mail]>
Signed-off-by: Behan Webster <[e-mail]>
Signed-off-by: Russell King <[e-mail]>

arch/arm/include/asm/percpu.h

···
 static inline unsigned long __my_cpu_offset(void)
 {
 	unsigned long off;
-	register unsigned long *sp asm ("sp");
 
 	/*
 	 * Read TPIDRPRW.
 	 * We want to allow caching the value, so avoid using volatile and
 	 * instead use a fake stack read to hazard against barrier().
 	 */
-	asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off) : "Q" (*sp));
+	asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off)
+		: "Q" (*(const unsigned long *)current_stack_pointer));
 
 	return off;
 }