iio: accel: BMC150: fix scale value for 16G

According to documentation ([1] - page 27), the range for 16G is
7.81mg/LSB. Converted to SI, this is:
    7.81 * 10^-3 * 9.80665 m/s^2 / LSB = 0.0765899365 m/s^2 / LSB

[1] http://ae-bst.resource.bosch.com/media/products/dokumente/bmc150/BST-BMC150-DS000-04.pdf



Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>