CRAS: alsa jack - fix device index lookup.
CRAS: alsa jack - fix device index lookup.

ARRAY_SIZE returns strlen+1 because of null so subtract that one.

BUG=none
TEST=alsa_jack_unittest

Change-Id: I07c9442dd6f2aaaf141ad59b8922787e019b9e2e
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

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