drm/amd/display: reduce else-if to else in dcn10_blank_pixel_data()

checkpatch reports
drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c:2902:13: style:
  Expression is always true because 'else if' condition is opposite to previous condition at line 2895. [multiCondition]
 } else if (blank) {
            ^
drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c:2895:6: note: first condition
 if (!blank) {
     ^
drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c:2902:13: note: else if condition is opposite to first condition
 } else if (blank) {

It is not necessary to explicitly the check != condition, an else is simplier.

Fixes: aa5a5777 ("drm/amd/display: Vari-bright looks disabled near end of MM14")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>