drm/amd/display: Fix uninitialized variables in dcn401

[WHAT & HOW]
surf_linear_128_l/c are used in CalculateBytePerPixelAndBlockSizes
before they are assigned, so initializing them before passing them into
the function.

This fixes 2 UNINIT issues reported by Coverity.

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>