mkimage: Fix strict-aliasing compiler warning

Version 4.2.4 of gcc produces the following warnings without this change:
  mkimage.c: In function ‘main’:
  mkimage.c:204: warning: dereferencing type-punned pointer will break strict-aliasing rules
  mkimage.c:222: warning: dereferencing type-punned pointer will break strict-aliasing rules

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>

tools/mkimage.c

@@ -145,7 +145,7 @@ main (int argc, char **argv)
 {
 	int ifd = -1;
 	struct stat sbuf;
-	unsigned char *ptr;
+	char *ptr;
 	int retval = 0;
 	struct image_type_params *tparams = NULL;
 
@@ -201,8 +201,7 @@ main (int argc, char **argv)
 			case 'a':
 				if (--argc <= 0)
 					usage ();
-				params.addr = strtoul (*++argv,
-					(char **)&ptr, 16);
+				params.addr = strtoul (*++argv, &ptr, 16);
 				if (*ptr) {
 					fprintf (stderr,
 						"%s: invalid load address %s\n",
@@ -219,8 +218,7 @@ main (int argc, char **argv)
 			case 'e':
 				if (--argc <= 0)
 					usage ();
-				params.ep = strtoul (*++argv,
-						(char **)&ptr, 16);
+				params.ep = strtoul (*++argv, &ptr, 16);
 				if (*ptr) {
 					fprintf (stderr,
 						"%s: invalid entry point %s\n",