staging: unisys: visorbus: visorbus_main.c: remove extra checks for dev->visorchannel

Removed checks for dev->visorchannel in visorbus_release_device()
and visorbus_remove_instance() since it is also checked in the
visorchannel_destroy() function.

Signed-off-by: Sameer Wadgaonkar <sameer.wadgaonkar@unisys.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>