IB/hfi1: Remove extra brackets from an if

A recent patch to hfi1 left behind a checkpatch error.

Fixes: fb24ea52 ("drivers: Remove explicit invocations of mmiowb()")
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>