sh: fix up fallout from syscall arg constification.

sys_execve() now takes a const pointer, so reflect this change where the
syscall is actually defined, too. Fixes up a build error due to prototype
mismatch.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/process_32.c

@@ -296,7 +296,8 @@ asmlinkage int sys_vfork(unsigned long r4, unsigned long r5,
 /*
  * sys_execve() executes a new program.
  */
-asmlinkage int sys_execve(char __user *ufilename, char __user * __user *uargv,
+asmlinkage int sys_execve(const char __user *ufilename,
+			  char __user * __user *uargv,
 			  char __user * __user *uenvp, unsigned long r7,
 			  struct pt_regs __regs)
 {