fusion: mptsas, fix lock imbalance

Fix two typos in mptsas_not_responding_devices. It was mutex_lock instead
of unlock.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Acked-by: "Desai, Kashyap" <Kashyap.Desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>