drm/amd/display: change when to set tap_hardcode_coeff

Set hardcode_coeff only when BOTH chroma and luma taps are
more than 1

without this underscan with h or v set to 0 darkens
the screen (either h or v set to 0, not both)

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>