wifi: plfxlc: fix potential memory leak in __lf_x_usb_enable_rx()

In the Linux kernel, the following vulnerability has been resolved: wifi: plfxlc: fix potential memory leak in __lf_x_usb_enable_rx() urbs does not be freed in exception paths in __lf_x_usb_enable_rx(). That will trigger memory leak. To fix it, add kfree() for urbs within "error" label. Compile tested only.