arm64: atomic64_dec_if_positive: fix incorrect branch condition

If we attempt to atomic64_dec_if_positive on INT_MIN, we will underflow
and incorrectly decide that the original parameter was positive.

This patches fixes the broken condition code so that we handle this
corner case correctly.
Reviewed-by: Steve Capper <steve.capper@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/atomic_ll_sc.h

@@ -159,7 +159,7 @@ __LL_SC_PREFIX(atomic64_dec_if_positive(atomic64_t *v))
 "	prfm	pstl1strm, %2\n"
 "1:	ldxr	%0, %2\n"
 "	subs	%0, %0, #1\n"
-"	b.mi	2f\n"
+"	b.lt	2f\n"
 "	stlxr	%w1, %0, %2\n"
 "	cbnz	%w1, 1b\n"
 "	dmb	ish\n"

arch/arm64/include/asm/atomic_lse.h

@@ -291,7 +291,7 @@ static inline long atomic64_dec_if_positive(atomic64_t *v)
 	/* LSE atomics */
 	"1:	ldr	x30, %[v]\n"
 	"	subs	%[ret], x30, #1\n"
-	"	b.mi	2f\n"
+	"	b.lt	2f\n"
 	"	casal	x30, %[ret], %[v]\n"
 	"	sub	x30, x30, #1\n"
 	"	sub	x30, x30, %[ret]\n"