regulator: lp3971 - remove unnecessary ret value checking in lp3971_i2c_write()

We already check count value before calling i2c_smbus_read_byte_data(),
no need to check it again.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>