drm/amdgpu/mes12: optimize MES pipe FW version fetching

Don't fetch it again if we already have it.  It seems the
registers don't reliably have the value at resume in some
cases.

Fixes: 785f0f9f ("drm/amdgpu: Add mes v12_0 ip block support (v4)")
Reviewed-by: Shaoyun.liu <Shaoyun.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>