drm/amd/display: Ignore wrong tautological warning

Some of our HW calcs functions compares a var against
itself to check for NaN. Gcc isn't fond of it and wrongfully
warns about a tautological comparison. Disable this check
for dcn_calcs_math.c.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>