staging: unisys: BUG halt on error in I/O channel

We precheck that we have enough space in an iochannel prior to writing to
it when we send in a fragmented skb.  Given that there is no recovery from
this condition that I can see, turn it into a BUG halt

Signed-off-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>