MIPS: o32: Fix number of arguments to splice(2).

The syscall code was assuming splice only takes 4 arguments so no stack
arguments were being copied from the userspace stack to the kernel stack.
As the result splice was likely to fail with EINVAL.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/scall32-o32.S

@@ -624,7 +624,7 @@ einval:	li	v0, -ENOSYS
 	sys	sys_pselect6		6
 	sys	sys_ppoll		5
 	sys	sys_unshare		1
-	sys	sys_splice		4
+	sys	sys_splice		6
 	sys	sys_sync_file_range	7	/* 4305 */
 	sys	sys_tee			4
 	sys	sys_vmsplice		4