msm_fb: display: Remove unnecessary dtv_pipe checks

In case of PAN display, PAN update function would return
without allocating dtv pipe resulting in no HDMI display.
This change removes unnecessary checks and enable dtv pipe
for PAN display as well.

CRs-Fixed: 379625
Change-Id: I533392a1120a21e962fbbbf0c07a89997832406f
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>