msm: mdss: dp: fix handling of EDID extension blocks

Current implementation assumes that the first extension
block of the EDID data always has the CEA extension tag.
This is incorrect and can lead to incorrect parsing of
resolution data. Fix this by removing the hardcoding of
the extension tag for the first extension block.

CRs-Fixed: 2027108
Change-Id: I5ef4cdb186591e291b2217db7ccec6f942d79ca4
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>