disp: msm: dp: use correct lane_count to validate mode

The lane_count used for validating the display mode
to be set is wrongly taken from the initial panel
capability. So, when lane count is reduced during
link training, the reduced lane count will not be
considered for validating supported modes. Hence
reporting incorrect display modes.

This change will use the correct lane count which
is obtained after the link training sequence.

Change-Id: Iab6239280c29961f7bc6f945ff3ecee9954b0b73
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>