Staging / IIO fixes for 3.15-rc4

Here are some small IIO driver fixes for 3.15-rc4 that resolve some
reported issues.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Merge tag 'iio-fixes-for-3.15b' of git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio into staging-linus

Jonathan writes:

Second set of fixes for IIO in the 3.15 cycle.

* ad2s1200 - Fix some missing parenthesis in a for statement that could have
  led to an error being missed when getting gpios.
* Fix a null derefference issue in the mpu6050 when platform data is not
  provided (or is provided via the device tree for example).
* exynos_adc bug on remove due to child devices having been added to the
  parent of the IIO device rather than the IIO device itself.  This caused an
  issue with the IIO device removing itself in it's remove function.
* Make all ADC drivers buildable as modules to avoid dependency issues if
  the IIO core is itself built as a module.  The exynos adc bug became
  apparently whilst this fix was being tested.