csky: Fixup remove duplicate irq_disable

Interrupt has been disabled in __schedule() with local_irq_disable()
and enabled in finish_task_switch->finish_lock_switch() with
local_irq_enabled(), So needn't to disable irq here.
Signed-off-by: Liu Yibin <jiulong@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/kernel/entry.S

@@ -332,8 +332,6 @@ ENTRY(__switch_to)
 
 	mfcr	a2, psr			/* Save PSR value */
 	stw	a2, (a3, THREAD_SR)	/* Save PSR in task struct */
-	bclri	a2, 6			/* Disable interrupts */
-	mtcr	a2, psr
 
 	SAVE_SWITCH_STACK