usb: dwc2/gadget: move phy bus legth initialization

This patch moves the part of code that initializes the PHY bus width.
This results in simpler code and removes the need to check whether
the Generic PHY Framework is used.

Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Robert Baldyga <r.baldyga@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>