drm/msm/sde: allow PP buffer overflow irq disable after encoder disable

Remove clone mode check when enabling or disabling write back ping-pong
buffer overflow IRQs. This allows sde encoder to disable pp buffer overflow
irq after physical encoder disable call.

Change-Id: I9372ac7c1a01dc6770d8f4692752a27e3630dd61
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>