staging: unisys: visorchannel: Make visorchannel_create take a gfp_t

This allows the caller to specify an appropriate GFP flag instead of
hardcoding the lowest common denominator.

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