drivers: usb_dc_nrfx: Align with nrfx version 1.4.0

A typo in the name of the bmRequest field in the nrfx_usbd_setup_t
structure was fixed in nrfx version 1.4.0. Update the driver to use
the new correct name: bRequest.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>