powerpc/xmon: Fiddle xmon_depth_to_print logic in xmon_show_stack()

Currently xmon_depth_to_print is static and global, but it's only
ever used in xmon_show_stack().

At least with a modern compiler it's inlined, so there's no point
in it being static, we could #define it but it's only used in one
place.

By reworking the logic we can drop count and just decrement the
max value as a loop counter. Also switch to a while loop so we
actually print no more than 64 frames as you'd expect based on the
variable name.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/xmon/xmon.c

@@ -1281,21 +1281,19 @@ static void get_function_bounds(unsigned long pc, unsigned long *startp,
 	catch_memory_errors = 0;
 }
 
-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))
 
 static void xmon_show_stack(unsigned long sp, unsigned long lr,
 			    unsigned long pc)
 {
+	int max_to_print = 64;
 	unsigned long ip;
 	unsigned long newsp;
 	unsigned long marker;
-	int count = 0;
 	struct pt_regs regs;
 
-	do {
+	while (max_to_print--) {
 		if (sp < PAGE_OFFSET) {
 			if (sp != 0)
 				printf("SP (%lx) is in userspace\n", sp);
@@ -1366,7 +1364,7 @@ static void xmon_show_stack(unsigned long sp, unsigned long lr,
 			break;
 
 		sp = newsp;
-	} while (count++ < xmon_depth_to_print);
+	}
 }
 
 static void backtrace(struct pt_regs *excp)