regulator: palmas: Squelch sparse warnings

convert to static variables to squelch the following sparse warnings:
drivers/regulator/palmas-regulator.c:325:36: warning: symbol 'palma_sleep_req_info' was not declared. Should it be static?
drivers/regulator/palmas-regulator.c:1414:32: warning: symbol 'palmas_ddata' was not declared. Should it be static?
drivers/regulator/palmas-regulator.c:1427:32: warning: symbol 'tps65917_ddata' was not declared. Should it be static?

Signed-off-by: Nishanth Menon <nm@ti.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>