RDMA/qib: Remove superfluous fallthrough statements

Commit 36a8f01c ("IB/qib: Add congestion control agent
implementation") erroneously marked a couple of switch cases as /*
FALLTHROUGH */, which were later converted to fallthrough statements by
commit df561f66 ("treewide: Use fallthrough pseudo-keyword"). This
triggered a Coverity warning about unreachable code.

Remove the fallthrough statements.

Link: https://lore.kernel.org/r/20200825171242.448447-1-alex.dewar90@gmail.com
Addresses-Coverity: ("Unreachable code")
Fixes: 36a8f01c

 ("IB/qib: Add congestion control agent implementation")
Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>