iio: bmc150: change sampling frequency

Currently driver reports device bandwidth list as available
sampling frequency. But sampling frequency is actually twice
the device bandwidth. This patch fixes this issue.

Signed-off-by: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@intel.com>
Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>