x86: Fixed NULL function pointer dereference in AMD microcode patch loader.

Dereference took place in code part responsible for manual installation
of microcode patches through /dev/cpu/microcode.

Signed-off-by: Peter Oruba <peter.oruba@amd.com>
Cc: Peter Oruba <peter.oruba@amd.com>
Cc: Tigran Aivazian <tigran@aivazian.fsnet.co.uk>
Signed-off-by: Ingo Molnar <mingo@elte.hu>