staging: iio: cdc: simplify return flow

Simplify return flow ad7150_write_event_params in order to reduce code length.
Since i2c_smbus_write_word_data only returns a negative value or 0 the change is safe.

This patch fixes the following coccicheck warning:

drivers/staging/iio/cdc/ad7150.c:182:2-5: WARNING: end returns can be simpified if negative or 0 value

Signed-off-by: Ioana Ciornei <ciorneiioana@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>