ASoC: isabelle: Remove regmap_exit()

With devm_ APIs regmap_exit() not needed, so remove regmap_exit().

Signed-off-by: Vishwas A Deshpande <vishwas.a.deshpande@ti.com>
Signed-off-by: M R Swami Reddy <mr.swami.reddy@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>