x86/microcode/amd: Remove unneeded pointer arithmetic

Remove unneeded pointer increment arithmetic, the pointer is
set at the beginning of the loop.

Signed-off-by: Nathan Fontenot <nathan.fontenot@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230502174232.73880-1-nathan.fontenot@amd.com