uboot-phytec

cmd: fpga: Cleanup error handling in connection to FPGA_NONE

Incorrect command is already handled and FPGA_NONE should be used only
one. In case of error CMD_RET_USAGE can be returned directly without any
addition logic around.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>