Staging: hv: Channel.c: fix up compiler warning

In the series of ASSERT removals, somehow we ended up with a compiler
warning in Channel.c.  This patch fixes that up.

Cc: Bill Pemberton <wfp5p@virginia.edu>
Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>