[MIPS] Remove stray .set mips3 resulting in 64-bit instruction in 32-bit kernels.

    
Only the NMI handler was affected so this is a low impact bug.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/genex.S

@@ -233,11 +233,11 @@ NESTED(except_vec_nmi, 0, sp)
 NESTED(nmi_handler, PT_SIZE, sp)
 	.set	push
 	.set	noat
-	.set	mips3
 	SAVE_ALL
  	move	a0, sp
 	jal	nmi_exception_handler
 	RESTORE_ALL
+	.set	mips3
 	eret
 	.set	pop
 	END(nmi_handler)