h8300: Fix missing consts in kernel_execve()

Fix missing consts in h8300's kernel_execve():

  arch/h8300/kernel/sys_h8300.c: In function 'kernel_execve':
  arch/h8300/kernel/sys_h8300.c:59: warning: initialization from incompatible pointer type
  arch/h8300/kernel/sys_h8300.c:60: warning: initialization from incompatible pointer type
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/h8300/kernel/sys_h8300.c

@@ -56,8 +56,8 @@ int kernel_execve(const char *filename,
 		  const char *const envp[])
 {
 	register long res __asm__("er0");
-	register char *const *_c __asm__("er3") = envp;
-	register char *const *_b __asm__("er2") = argv;
+	register const char *const *_c __asm__("er3") = envp;
+	register const char *const *_b __asm__("er2") = argv;
 	register const char * _a __asm__("er1") = filename;
 	__asm__ __volatile__ ("mov.l %1,er0\n\t"
 			"trapa	#0\n\t"