sparc64: perf: Use UREG_FP rather than UREG_I6

perf walks userspace callchains by following frame pointers. Use the
UREG_FP macro to make it clearer that the %fp is being used.
Signed-off-by: David Ahern <david.ahern@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/kernel/perf_event.c

@@ -1756,7 +1756,7 @@ static void perf_callchain_user_64(struct perf_callchain_entry *entry,
 {
 	unsigned long ufp;
 
-	ufp = regs->u_regs[UREG_I6] + STACK_BIAS;
+	ufp = regs->u_regs[UREG_FP] + STACK_BIAS;
 	do {
 		struct sparc_stackf __user *usf;
 		struct sparc_stackf sf;
@@ -1780,7 +1780,7 @@ static void perf_callchain_user_32(struct perf_callchain_entry *entry,
 {
 	unsigned long ufp;
 
-	ufp = regs->u_regs[UREG_I6] & 0xffffffffUL;
+	ufp = regs->u_regs[UREG_FP] & 0xffffffffUL;
 	do {
 		unsigned long pc;