ASoC: pxa: Remove superfluous locking

The locking here was added in commit 71a29560 ("ASoC: Lock the CODEC in PXA
external jack controls") to protect the DAPM changes that are made inside of
${board}_ext_control() against concurrent updates. The ASoC core was updated in
commit a73fb2df ("ASoC: dapm: Use DAPM mutex for DAPM ops instead of codec
mutex") to use a card wide lock rather the CODEC mutex to protect DAPM
operations. We now have proper locking inside ${board}_ext_control() itself, so
taking the CODEC lock can be removed.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>