a double unlock in get_chip. get_chip is called with
chip->mutex held and caller is responsible for unlocking it too.

Do not unlock the lock in get_chip on a fail path. This would mean
a double unlock.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
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