power: supply: sbs-battery: Add delay when changing capacity mode bit

At least with the Inspired Energy compatible batteries a delay is required
after setting the capacity mode bit from amp to watts or the reverse.
Setting the bit and then immediately pooling the status register results
in an unknown error being returned in the register. Add the delay results
in and ok status being return. This was also seen when reading the charge
and energy registers where the wrong value was returned for the requested
mode.

Signed-off-by: Phil Reid <preid@electromag.com.au>
Tested-by: Michael Heinemann <committed@heine.so>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>