uboot-imx

menu: Return an error code if Ctrl-C is pressed

Previously, if the menu activated by the 'sysboot' command gets
interrupted by a Ctrl-C, the behaviour is as if the menu timeout was
reached - i.e. boot the default menu entry. This patch fixes that
so a Ctrl-C now terminates the command as the user would expect.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
Reviewed-by: Simon Glass <sjg@chromium.org>