irqchip/irq-alpine-msi: Release the correct domain on error

The "msi_domain" variable is NULL here so it leads to a NULL dereference.  It
looks like we actually intended to free "middle_domain".

Fixes: e6b78f2c ('irqchip: Add the Alpine MSIX interrupt controller')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Antoine Tenart <antoine.tenart@free-electrons.com>
Cc: kernel-janitors@vger.kernel.org
Cc: Tsahee Zidenberg <tsahee@annapurnalabs.com>
Link: http://lkml.kernel.org/r/20160311081442.GE31887@mwanda


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>