BACKPORT: FROMLIST: platform/loongarch: laptop: Get brightness setting from EC on probe

Previously 1 is unconditionally taken as current brightness value. This
causes problems since it's required to restore brightness settings on
resumption, and a value that doesn't match EC's state before suspension
will cause surprising changes of screen brightness.

Let's get brightness from EC and take it as the current brightness on
probe of the laptop driver to avoid the surprising behavior. Tested on
TongFang L860-T2 3A5000 laptop.

Cc: [email protected]
Fixes: 6246ed0 ("LoongArch: Add ACPI-based generic laptop driver")
Signed-off-by: Yao Zi <[email protected]>

Link: https://lore.kernel.org/loongarch/[email protected]/
Signed-off-by: Mingcong Bai <[email protected]>

Author: ziyao233

drivers/platform/loongarch/loongson-laptop.c

@@ -392,7 +392,7 @@ static int laptop_backlight_register(void)
 	if (!acpi_evalf(hotkey_handle, &status, "ECLL", "d"))
 		return -EIO;
 
-	props.brightness = 1;
+	props.brightness = ec_get_brightness();
 	props.max_brightness = status;
 	props.type = BACKLIGHT_PLATFORM;