drm/amdgpu:/navi10: use the ODCAP enum to index the caps array

Rather than the FEATURE_ID flags.  Avoids a possible reading past
the end of the array.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Reported-by: Aleksandr Mezin <mezin.alexander@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 5.5.x