arch/ppc: Replace custom macro with isdigit()

diff -urpN -X dontdiff linux-2.6.13/arch/ppc/boot/common/misc-common.c linux-2.6.13~macro_removal/arch/ppc/boot/common/misc-common.c
@@ -16,6 +16,7 @@
 
 #include <stdarg.h>	/* for va_ bits */
 #include <linux/config.h>
+#include <linux/ctype.h>
 #include <linux/string.h>
 #include <linux/zlib.h>
 #include "nonstdio.h"

@@ -301,8 +302,6 @@ _printk(char const *fmt, ...)
 	return;
 }
 
-#define is_digit(c) ((c >= '0') && (c <= '9'))
-
 void
 _vprintk(void(*putc)(const char), const char *fmt0, va_list ap)
 {

@@ -329,7 +328,7 @@ _vprintk(void(*putc)(const char), const 
 			{
 				zero_fill = FALSE;
 			}
-			while (is_digit(c))
+			while (isdigit(c))
 			{
 				left_prec = (left_prec * 10) + (c - '0');
 				c = *fmt0++;

@@ -338,7 +337,7 @@ _vprintk(void(*putc)(const char), const 
 			{
 				c = *fmt0++;
 				zero_fill++;
-				while (is_digit(c))
+				while (isdigit(c))
 				{
 					right_prec = (right_prec * 10) + (c - '0');
 					c = *fmt0++;