usb: dwc2: Bits in bitfield should add up to 32

The unioned u32 is used for clearing etc. Having the number of
bitfield bits add up to more than 32 is broken, even if benign.

Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Charles Manning <cdhmanning@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>