usb: zynqmp: Fix build warnings

The driver does "return 0" in function with void type.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
1 file changed