uboot-imx

usb: fastboot: fix potential buffer overflow

cb_getvar tries to prevent overflowing the response buffer
by using strncat. But strncat takes the number of data bytes
copied as a limit not the total buffer length so it can still
overflow. Pass the correct value instead.

cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
cc: Rob Herring <robh@kernel.org>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>