amd64_edac: fix DRAM base and limit extraction

On Fam10h and above, F1x[1, 0][7C:40] are DRAM Base/Limit registers
which specify the destination node of a DRAM address. Those address
boundaries are being extracted into ->dram_base[] and ->dram_limit[].
Correct the extraction masks to match the respective address bits.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>