drm/amdgpu: Fix uvd firmware version information for vega20 (v2)

The uvd version information was not set correctly for vega20.
Rearrange the logic to set it correctly and fix the warnings
as a result.

v2: fix version formatting for userspace based on feedback from Leo

Fixes: 96ca7f298f (drm/amdgpu/vg20:support new UVD FW version naming convention)
Reviewed-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>