regulator: Include err.h from consumer.h to fix build failure

regulator: Include err.h from consumer.h to fix build failure

sh:sh2007_defconfig fails to build with the following error:

In file included from include/linux/regulator/machine.h:18:0,
                 from arch/sh/boards/board-sh2007.c:10:
include/linux/regulator/consumer.h: In function 'regulator_get_optional':
include/linux/regulator/consumer.h:271:2:
		error: implicit declaration of function 'ERR_PTR'
include/linux/err.h: At top level:
include/linux/err.h:23:35: error: conflicting types for 'ERR_PTR'
include/linux/regulator/consumer.h:271:9:
		note: previous implicit declaration of 'ERR_PTR' was here

Since consumer.h uses ERR_PTR, it should include err.h.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Mark Brown <broonie@kernel.org>