x86, microcode, AMD: Remove unneeded memset call

collect_cpu_info_amd() clears its csig arg but this is done in the
microcode_core's collect_cpu_info() by clearing the embedding struct
ucode_cpu_info. Drop it.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
Acked-by: Andreas Herrmann <Andreas.Herrmann3@amd.com>