dt-bindings: usb: xilinx: Replace Manish by Piyush

Manish no longer works for AMD/Xilinx and there is also no activity from
him. That's why proposing Piyush as the best candidate instead.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/504444f5c2f4e725ac39cba1d72032d5a00c7cda.1684828805.git.michal.simek@amd.com