drm/amd/display: remove duplicated comparison expression

There is comparison expression that is duplicated and hence one
of the expressions can be removed.  Remove it.

Addresses-Coverity: ("Same on both sides")
Fixes: 12e2b2d4 ("drm/amd/display: add dcc programming for dual plane")
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>