power_supply: bq27x00: remove double endian swap

The bq27x00 registers are little endian, so just read them as such
and don't do double endian swap on LE machines.

This also gets rid of strange looking shift that was done after
reading 8bit register because endian swap in bq27x00_read() was
messing it up.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>