regulator: aat2870-regulator.c needs module.h

aat2870-regulator.c needs to include linux/module.h to fix multiple
build errors.

drivers/regulator/aat2870-regulator.c:145: error: 'THIS_MODULE' undeclared here (not in a function)
drivers/regulator/aat2870-regulator.c:230: warning: type defaults to 'int' in declaration of 'MODULE_DESCRIPTION'
drivers/regulator/aat2870-regulator.c:231: warning: type defaults to 'int' in declaration of 'MODULE_LICENSE'
drivers/regulator/aat2870-regulator.c:232: warning: type defaults to 'int' in declaration of 'MODULE_AUTHOR'

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>