disp: msm: sde: fix encoder parsing in atomic_check phase

During atomic_check phase the encoder_mask is taken
from old crtc->state leading to wrong validation.
Fix it by taking the encoder_mask from new crtc state.

Change-Id: Ifcfc4bee887168d8208ffdafb1cf5ea4c4473796
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>