iw_cxgb4: Convert a __force cast

__force casts should be avoided if there is a better alternative.
Hence modify the comparison of s_addr with INADDR_ANY such that the
__force cast is no longer necessary.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Steve Wise <swise@opengridcomputing.com>
Cc: Vipul Pandya <vipul@chelsio.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>