power:bq27xxx: 27000/10 read FLAGS register as single

The bq27000 and bq27010 have a single byte FLAGS register.
Other gauges have 16 bit FLAGS registers.

For reading the FLAGS register it is sufficient to read the single
register instead of reading RSOC at the next higher address as
well and then ignore the high byte.

This does not change functionality but optimizes i2c and hdq
traffic.

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Acked-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>