[AVR32] Fix wrong pt_regs in critical exception handler

It's not like it really matters at this point since the system is
dying anyway, but handle_critical pushes too few registers on the
stack so the register dump, which makes the register dump look a bit
strange. This patch fixes it.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/kernel/entry-avr32b.S

@@ -316,8 +316,8 @@ save_full_context_ex:
 
 	/* Low-level exception handlers */
 handle_critical:
-	pushm	r12
-	pushm	r0-r12
+	sub	sp, 4
+	stmts	--sp, r0-lr
 	rcall	save_full_context_ex
 	mfsr	r12, SYSREG_ECR
 	mov	r11, sp