ab8500-charger: Do not touch VBUSOVV bits

Do not touch the VBUSOVV in USBCHTRL2 when running on AB8505.

Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Marcus COOPER <marcus.xm.cooper@stericsson.com>
Tested-by: Mian Yousaf KAUKAB <mian.yousaf.kaukab@stericsson.com>