IB/ipath: Fix bad argument to clear_bit()

Code was converted from a &= ~mask to clear_bit, but the bit was left
shifted instead of being used directly, so we were either trashing
memory several pages away, or sometimes taking a kernel page fault on
an invalid page.

Signed-off-by: Dave Olson <dave.olson@qlogic.com>
Signed-off-by: Bryan O'Sullivan <bryan.osullivan@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>