OvmfPkg: fix the mask for accessing the PIIX4 PMBA [15:6] bitfield

The Index Register Base Address bitfield is selected by the binary mask
00000000 00000000 11111111 11000000, 0xFFC0; fix the typo.

Reported-by: Gleb Natapov <gleb@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13720 6f19259b-4bc3-4df7-8a09-765794883524
2 files changed