yocto: slides: Fix the description of SERIAL_CONSOLES

The SERIAL_CONSOLES variable isn't used for the kernel commandline, but
to configure getty.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

slides/yocto-bsp/yocto-bsp.tex

@@ -78,7 +78,7 @@ \subsection{Hardware configuration files}
     \item[MACHINE\_FEATURES] List of hardware features provided by the
       machine, e.g. \code{usbgadget usbhost screen wifi}
     \item[SERIAL\_CONSOLES] Speed and device for the serial console to
-      attach. Passed to the kernel as the \code{console} parameter,
+	    attach. Used to configure \code{getty},
       e.g. \code{115200;ttyS0}
     \item[KERNEL\_IMAGETYPE] The type of kernel image to build, e.g.
       \code{zImage}