hwmon: (w83627ehf) Use proper exit sequence

According to the datasheet for Winbond W83627DHG the proper way to exit
the Extended Function Mode is to write 0xaa to the EFER(0x2e or 0x4e).

Signed-off-by: Jonas Jonsson <jonas@ludd.ltu.se>
Signed-off-by: Jean Delvare <khali@linux-fr.org>