powerpc/xmon: Use STACK_FRAME_OVERHEAD in xmon_show_stack()

We use STACK_FRAME_OVERHEAD in the exception vectors to establish
the exception frame, so it should be good enough to use here.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/xmon/xmon.c

@@ -1286,12 +1286,6 @@ static int xmon_depth_to_print = 64;
 #define LRSAVE_OFFSET		(STACK_FRAME_LR_SAVE * sizeof(unsigned long))
 #define MARKER_OFFSET		(STACK_FRAME_MARKER * sizeof(unsigned long))
 
-#ifdef __powerpc64__
-#define REGS_OFFSET		0x70
-#else
-#define REGS_OFFSET		16
-#endif
-
 static void xmon_show_stack(unsigned long sp, unsigned long lr,
 			    unsigned long pc)
 {
@@ -1355,10 +1349,10 @@ static void xmon_show_stack(unsigned long sp, unsigned long lr,
 		   an exception frame. */
 		if (mread(sp + MARKER_OFFSET, &marker, sizeof(unsigned long))
 		    && marker == STACK_FRAME_REGS_MARKER) {
-			if (mread(sp + REGS_OFFSET, &regs, sizeof(regs))
+			if (mread(sp + STACK_FRAME_OVERHEAD, &regs, sizeof(regs))
 			    != sizeof(regs)) {
 				printf("Couldn't read registers at %lx\n",
-				       sp + REGS_OFFSET);
+				       sp + STACK_FRAME_OVERHEAD);
 				break;
 			}
 			printf("--- Exception: %lx %s at ", regs.trap,