grub.cfg: set serialno for boot_fat.uefi.img

set it to fixed 0123456789 so that we could see the serial number
correctly when we flash with boot_fat.uefi.img for development

Otherwise what we see is something like this:
$ adb devices
List of devices attached
(no serial number)  device

$

Test: adb devices

Change-Id: I2bdb00ddc513f9b64716f823618d38735c7e43d4
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
1 file changed