Add back accidentally dropped masking...

• PCI_MASK_CONFIG(sc->dev, CBBR_BRIDGECTRL,
• & ~CBBM_BRIDGECTRL_INTR_IREQ_ISA_EN, 2);

was accidentally dropped from r355822 in the refactor. Restore it since 16-bit
cards may fail without it (some bridges autodetect this properly, so my laptop
worked when I tested it).

Noticed by: rpokala@