usb: phy: ab8500-usb: fix unbalanced clock and regulator disable warnings

To prevent clock and regulator frameworks from complaining, only disable
the host or peripheral phy if they were enabled.

Reported-by: Sakethram Bommisetti <sakethram.bommisetti@stericsson.com>
Signed-off-by: Mian Yousaf Kaukab <mian.yousaf.kaukab@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>