msm: mdss: correct ubwc total plane size calc and usage

Total plane size was not calculated properly for ubwc formats.
Additional the value that this was compared against was also
not calculated properly. This change fixes some minor issues
in data validation.

Change-Id: I0a925f4824bf084e4a7465ecc650ea93936e8f68
Signed-off-by: Terence Hampson <thampson@codeaurora.org>