menu: fix the logic checking whether ESC key is pressed

menu: fix the logic checking whether ESC key is pressed

It's observed that the bootmenu on a serial console sometimes
incorrectly quitted with superfluous characters filled to command
line input:

>  *** U-Boot Boot Menu ***
>
>      1. Startup system (Default)
>      2. Upgrade firmware
>      3. Upgrade ATF BL2
>      4. Upgrade ATF FIP
>      5. Load image
>      0. U-Boot console
>
>
>  Press UP/DOWN to move, ENTER to select, ESC to quit
>MT7988> [B

Analysis shows it was caused by the wrong logic of bootmenu_loop:

At first the bootmenu_loop received the first ESC char correctly.

However, during the second call to bootmenu_loop, there's no data
in the UART Rx FIFO. Due to the low baudrate, the second char of
the down array key sequence hasn't be fully received.

But bootmenu_loop just did a mdelay(10), and then treated it as a
single ESC key press event. It didn't even try tstc() again after
the 10ms timeout.

This patch fixes this issue by letting bootmenu_loop check tstc()
twice.

Tested-By: E Shattow <lucent@gmail.com>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
Reviewed-by: Daniel Golle <daniel@makrotopia.org>
Tested-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Simon Glass <sjg@chromium.org>