MIPS: Fix error values in case of bad_stack

We want EFAULT, not -<syscall number>

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1699/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/scall32-o32.S

@@ -169,7 +169,7 @@ stackargs:
 	 * We probably should handle this case a bit more drastic.
 	 */
 bad_stack:
-	negu	v0				# error
+	li	v0, EFAULT
 	sw	v0, PT_R2(sp)
 	li	t0, 1				# set error flag
 	sw	t0, PT_R7(sp)