asus/m4a785t-m: correct the CPU microcode patch selection

asus/m4a785t-m: correct the CPU microcode patch selection

Thanks to ruik on #coreboot Freenode IRC channel for
  explaining to me how to get the cpu revision:
    Feb 21 22:07:32 <ruik>  ruik@ruik:~/coreboot$ cpuid | grep ^00000001
    Feb 21 22:07:32 <ruik>  00000001 00020f32 00020800 00000001 178bfbff
    [..]
    Feb 21 22:07:44 <ruik>  the 20f32 is mine CPUID
The rest was just looking at the correspondance in
  src/cpu/amd/model_10xxx/update_microcode.c
  like Marc Jones explained(thanks Marc Jones) in the mailing list here:
  http://www.coreboot.org/pipermail/coreboot/2012-February/068332.html

Change-Id: Ie0f004990e6b65456de009a4dcc306498bdb47e9
Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>
Reviewed-on: http://review.coreboot.org/669
Reviewed-by: Marc Jones <marcj303@gmail.com>
Tested-by: build bot (Jenkins)