IB/qib: Return correct MAD when setting link width to 255

Fix a bug which causes the driver to return incorrect MADs as a
response to Set(PortInfo) which sets the link width to 0xFF or link
speed to 0xF.

Signed-off-by: Mitko Haralanov <mitko@qlogic.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@qlogic.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>