odroid: usbhost - Add missing gpio_request call

The USB host code was missing gpio_request() calls before using the gpio
functions, causing errors to be printed out.

As a side note calls to max77686_set_buck_mode(OPMODE_OFF/OPMODE_ON) have
been removed, as they did not have any effect. This is as per Przemyslaw:
I looked into the documentation and there is a "ENB8" pin in PMIC package.
This pin allows steering BUCK8 ON/OFF by the hardware. If ENB8 is set to low
then you can do on/off. If high, then you cannot change its state by I2C
write, which seems to be the case with the Odroids.

Signed-off-by: Suriyan Ramasami <suriyan.r@gmail.com>
Acked-by: Przemyslaw Marczak <p.marczak@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>