usb: gadget: udc-xilinx: fix incorrect type in assignment warning

The bitwise attribute is used by the sparse utility to make sure the
variable is converted to the local processor type before other (unsafe)
operations are performed on the variable. Fix the below sparse warnings
type casted with __le16:

warning: incorrect type in assignment (different base types)
   expected unsigned short [usertype]
   got restricted __le16 [usertype]

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/all/202209020044.CX2PfZzM-lkp@intel.com/
Signed-off-by: Piyush Mehta <piyush.mehta@amd.com>
Link: https://lore.kernel.org/r/20230822063201.16929-4-piyush.mehta@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>