IB/qib: Remove a set-but-not-used variable

This patch avoids that a compiler warning is reported when building with
W=1.

Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Fixes: 49c0e241

 ("IB/qib: Change SDMA progression mode depending on single- or multi-rail")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>