xtensa: re-wire umount syscall to sys_oldumount

commit 2651cc69 upstream.

Userspace actually passes single parameter (path name) to the umount
syscall, so new umount just fails. Fix it by requesting old umount
syscall implementation and re-wiring umount to it.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
[lizf: Backported to 3.4: adjust filename]
Signed-off-by: Zefan Li <lizefan@huawei.com>

arch/xtensa/include/asm/unistd.h

@@ -394,7 +394,8 @@ __SYSCALL(174, sys_chroot, 1)
 #define __NR_pivot_root 			175
 __SYSCALL(175, sys_pivot_root, 2)
 #define __NR_umount 				176
-__SYSCALL(176, sys_umount, 2)
+__SYSCALL(176, sys_oldumount, 1)
+#define __ARCH_WANT_SYS_OLDUMOUNT
 #define __NR_swapoff 				177
 __SYSCALL(177, sys_swapoff, 1)
 #define __NR_sync 				178