systemd-serialgetty: allow baud rate overriding

In case a getty is required on a UART which is not being
used as the kernel console, the current agetty invocation
fails to obey the baud rate configured through the
SERIAL_CONSOLES variable because it uses --keep-baud.

(From OE-Core rev: b54b73834e73d55de1038b55d0a4d7f49cda52d0)

Signed-off-by: Awais Belal <awais_belal@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/systemd/systemd-serialgetty/serial-getty@.service

@@ -21,7 +21,7 @@ IgnoreOnIsolate=yes
 
 [Service]
 Environment="TERM=xterm"
-ExecStart=-/sbin/agetty -8 -L --keep-baud %I @BAUDRATE@ $TERM
+ExecStart=-/sbin/agetty -8 -L %I @BAUDRATE@ $TERM
 Type=idle
 Restart=always
 RestartSec=0