iio: remove unused gpio consumer.h include

GPIO handling code has been removed from the drivers (since
this is now handled by the ACPI core) in commit 0f079650 ("iio:
remove gpio interrupt probing from drivers that use a single interrupt").

Remove the include for linux/gpio/consumer.h since it is no longer
used.

Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>