Staging: dgnc: Use goto for spinlock release before return

spin_unlock_irqrestore() is called at several
different places before exiting. This patch uses a goto statement
to factorize these calls.

Coccinelle was used to generate this patch.

Signed-off-by: Quentin Lambert <lambert.quentin@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>