RDMA/bnxt_re: Modify a fall-through annotation

This patch avoids that gcc reports the following warning when building
with W=1:

drivers/infiniband/hw/bnxt_re/ib_verbs.c:2404:4: warning: this statement may fall through [-Wimplicit-fallthrough=]

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>