devargs: fix parsing truncation when using format

Space for string terminating NUL character should be provided to
snprintf() to avoid the last symbol truncation.

Fixes: a23bc2c4e0 ("devargs: add non-variadic parsing function")

Reported-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Gaetan Rivet <gaetan.rivet@6wind.com>

lib/librte_eal/common/eal_common_devargs.c

@@ -285,7 +285,7 @@ rte_devargs_parsef(struct rte_devargs *da, const char *format, ...)
 	}
 
 	va_start(ap, format);
-	vsnprintf(dev, len, format, ap);
+	vsnprintf(dev, len + 1, format, ap);
 	va_end(ap);
 
 	return rte_devargs_parse(da, dev);