drm/msm/dp: remove mst connector properly during uninstall

In the mst connector uninstall function, the
previous implementation removed the connector
from the mst connector list using its id.
However, by the time the execution path reaches
this function, the id has already been cleared
from the connector data structure, therefore the
list never got cleared. To resolve this, the
connector should be identified using pointer
comparison. This patch also includes a small
change to the size of the input buffer for the
mst write edid modes function to allow for long
input configurations.

CRs-Fixed: 2328500
Change-Id: I4b1af0afdbb55542c8ddbc0751083ab7810be53f
Signed-off-by: Fuad Hossain <fhossain@codeaurora.org>