staging: unisys: visorbus: add error handling visorbus_enable_channel_interrupt

Add error handling to visorbus_enable_channel_interrupt.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>