UBUNTU: SAUCE: platform/x86: dell-uart-backlight: add missing status command

UBUNTU: SAUCE: platform/x86: dell-uart-backlight: add missing status command

BugLink: https://bugs.launchpad.net/bugs/1813877
DELL_UART_GET_SCALAR has been declared in
drivers/platform/x86/dell-uart-backlight.h, but its definition is
missing. It won't lead to issues on old AIO platforms, since this
command is newly introduced and is not supported by all old AIOs.

Signed-off-by: AceLan Kao <acelan.kao@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>