ACPI: thinkpad-acpi: update brightness sysfs interface support

Update the brightness sysfs interface (done through the backlight class) to
be in line with the rest of the thinkpad-acpi driver.

This renames the incorrect, un-obvious, and clash-prone name of "ibm" for
the backlight device to a much more fitting and descriptive
"thinkpad_screen".  This is something I wanted to do for quite a while...

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/misc/thinkpad_acpi.c b/drivers/misc/thinkpad_acpi.c
index ba749df..c0a023c 100644
--- a/drivers/misc/thinkpad_acpi.c
+++ b/drivers/misc/thinkpad_acpi.c
@@ -2414,8 +2414,9 @@
 	if (b < 0)
 		return b;
 
-	ibm_backlight_device = backlight_device_register("ibm", NULL, NULL,
-							 &ibm_backlight_data);
+	ibm_backlight_device = backlight_device_register(
+					TPACPI_BACKLIGHT_DEV_NAME, NULL, NULL,
+					&ibm_backlight_data);
 	if (IS_ERR(ibm_backlight_device)) {
 		printk(IBM_ERR "Could not register backlight device\n");
 		return PTR_ERR(ibm_backlight_device);