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>
diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index a665e3f..689db65 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -1756,7 +1756,7 @@
 {
 	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 @@
 {
 	unsigned long ufp;
 
-	ufp = regs->u_regs[UREG_I6] & 0xffffffffUL;
+	ufp = regs->u_regs[UREG_FP] & 0xffffffffUL;
 	do {
 		unsigned long pc;