IB/nes: Fix a compiler warning

Avoid that the following compiler warning is reported when building with
W=1:

drivers/infiniband/hw/nes/nes_hw.c:646:51: warning: suggest braces around empty body in an 'if' statement [-Wempty-body]

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