we read the IQ correction values (i_cal and q_cal) for G mode from a wrong
location (the same shifts as for A mode is applied which is incorrect). use
correct locations, matching the docs and HAL sources.

also we should write IQ correction only when we have that information in the
EEPROM, starting from version 4. also write it in the same way as we do in the
periodic recalibration (enable last), just to be sure.
Signed-off-by: Bruno Randolf <br1@einfach.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>