staging: unisys: include: Remove COVER macro from channel.h

Replaced the one and only call to COVER in iochannel.h.

Signed-off-by: Charles Daniels <cdaniels@fastmail.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: David Binder <david.binder@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>