iio:accel:stk8312: add triggered buffer dependency

Add the still missing dependencies for triggered buffer support.

Fixes: 	95c12bba ("iio: accel: Add buffer mode for Sensortek STK8312")

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>
Reviewed-by: Tiberiu Breana <tiberiu.a.breana@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>