proc: use named enums for better readability

Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

fs/proc/base.c

@@ -699,7 +699,7 @@ int proc_setattr(struct dentry *dentry, struct iattr *attr)
  */
 static bool has_pid_permissions(struct proc_fs_info *fs_info,
 				 struct task_struct *task,
-				 int hide_pid_min)
+				 enum proc_hidepid hide_pid_min)
 {
 	/*
 	 * If 'hidpid' mount option is set force a ptrace check,