regulator: add missing MODULE_DESCRIPTION() macro

regulator: add missing MODULE_DESCRIPTION() macro

On x86, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/regulator/da9121-regulator.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/regulator/max20411-regulator.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/regulator/rt4831-regulator.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/regulator/tps6286x-regulator.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240610-md-drivers-regulator-v2-1-cf39106d7e54@quicinc.com
Signed-off-by: Mark Brown <broonie@kernel.org>