arm64: make ll/sc __cmpxchg_case_##name asm consistent

The ll/sc __cmpxchg_case_##name assembly mostly uses symbolic names for
operands, but in a single case uses %2 to refer to what is otherwise
known as %[v]. This makes the code more painful to read than is
necessary.

Use %[v] instead.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/atomic_ll_sc.h

@@ -181,7 +181,7 @@ __LL_SC_PREFIX(__cmpxchg_case_##name(volatile void *ptr,		\
 	unsigned long tmp, oldval;					\
 									\
 	asm volatile(							\
-	"	prfm	pstl1strm, %2\n"				\
+	"	prfm	pstl1strm, %[v]\n"				\
 	"1:	ldxr" #sz "\t%" #w "[oldval], %[v]\n"			\
 	"	eor	%" #w "[tmp], %" #w "[oldval], %" #w "[old]\n"	\
 	"	cbnz	%" #w "[tmp], 2f\n"				\