media: drxd: drop offset var from DownloadMicrocode()

The offset is not needed, and it is never used, as the pointer
itself is already incremented.

So, drop it, in order to solve a W=1 clang warning.

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>