regmap: Provide __acquires/__releases annotations

Fix the following sparse warnings:

drivers/base/regmap/regmap.c:305:13: warning: context imbalance in 'regmap_lock_spinlock' - wrong count at exit
drivers/base/regmap/regmap.c:314:13: warning: context imbalance in 'regmap_unlock_spinlock' - unexpected unlock

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>