regulator: fix fatal kernel-doc error

Fix fatal kernel-doc error in <linux/regulator/driver.h>:

Error(include/linux/regulator/driver.h:52): cannot understand prototype: 'struct regulator_linear_range '

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
[Rewrote first line -- broonie]
Signed-off-by: Mark Brown <broonie@linaro.org>