usb: phy: phy-generic: Fix reset behaviour on legacy boot

The gpio-desc migration done in v4.0 caused a regression
with legacy boots due to reversed reset logic.
e.g. omap3-beagle USB host breaks on legacy boot.

Request the reset GPIO with GPIOF_ACTIVE_LOW flag so that
it matches the driver logic and pin behaviour.

Fixes: e9f2cefb ("usb: phy: generic: migrate to gpio_desc")
Cc: <stable@vger.kernel.org> # 4.0+
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>