Commit 36a8f01c ("IB/qib: Add congestion control agent
implementation") tries to store the value 1984 in a u8, which leads to
truncation.  Fix this by making the member big enough.

This bug was detected by a smatch warning.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NRamkrishna Vepa <ramkrishna.vepa@intel.com>
Signed-off-by: NMike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: NRoland Dreier <roland@purestorage.com>