x86, microcode_amd: fix shift warning

microcode_amd.c uses ">> 32" on a 32-bit value, so gcc warns about that.
The code could use something like this *untested* patch.

linux-next-20080821/arch/x86/kernel/microcode_amd.c:229: warning: right shift count >= width of type

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>