drm/amdgpu: Add double-sscanf but invert

Add back the double-sscanf so that both decimal
and hexadecimal values could be read in, but this
time invert the scan so that hexadecimal format
with a leading 0x is tried first, and if that
fails, then try decimal format.

Also use a logical-AND instead of nesting double
if-conditional.

See commit "drm/amdgpu: Fix a bug for input with double sscanf"

Cc: Alexander Deucher <Alexander.Deucher@amd.com>
Cc: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: John Clements <john.clements@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>