uml: fix compile warning

This fixes:
incompatible pointer type: => 89
arch/um/kernel/exec.c: warning: passing argument 2 of 'execve1' from
incompatible pointer type: => 69, 85
arch/um/kernel/exec.c: warning: passing argument 3 of 'execve1' from
incompatible pointer type: => 69, 85

which was introduced by d7627467b7a8d ("Make do_execve() take a const
filename pointer")

Signed-off-by: Richard Weinberger <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Jeff Dike <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/um/kernel/exec.c

···
 	return error;
 }
 
-long um_execve(const char *file, char __user *__user *argv, char __user *__user *env)
+long um_execve(const char *file, const char __user *const __user *argv, const char __user *const __user *env)
 {
 	long err;
 
···
 	return err;
 }
 
-long sys_execve(const char __user *file, char __user *__user *argv,
-		char __user *__user *env)
+long sys_execve(const char __user *file, const char __user *const __user *argv,
+		const char __user *const __user *env)
 {
 	long error;
 	char *filename;

arch/um/kernel/internal.h

···
-extern long um_execve(const char *file, char __user *__user *argv, char __user *__user *env);
+extern long um_execve(const char *file, const char __user *const __user *argv, const char __user *const __user *env);

arch/um/kernel/syscall.c

···
 
 	fs = get_fs();
 	set_fs(KERNEL_DS);
-	ret = um_execve(filename, (char __user *__user *)argv,
-			(char __user *__user *) envp);
+	ret = um_execve(filename, (const char __user *const __user *)argv,
+			(const char __user *const __user *) envp);
 	set_fs(fs);
 
 	return ret;