thinkpad-acpi: silence bogus warning when ACPI video is disabled

Make use of acpi_video_backlight_support() also in hotkey_init, to make
sure this doesn't happen:

thinkpad_acpi: This ThinkPad has standard ACPI backlight brightness
               control, supported by the ACPI video driver
thinkpad_acpi: Disabling thinkpad-acpi brightness events by default...
thinkpad_acpi: Standard ACPI backlight interface not available,
               thinkpad_acpi native brightness control enabled
thinkpad_acpi: detected a 16-level brightness capable ThinkPad

Note that this is purely cosmetic, there is absolutely _no_ change in
behaviour.  Those events are sometimes enabled at runtime by userspace, but
the driver never enables them by itself unless someone messed with the
default keymaps.
Signed-off-by: NHenrique de Moraes Holschuh <hmh@hmh.eng.br>
Reported-by: NJochen Schulz <jrschulz@well-adjusted.de>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -2655,7 +2655,7 @@ static int __init hotkey_init(struct ibm_init_struct *iibm)
 		/* update bright_acpimode... */
 		tpacpi_check_std_acpi_brightness_support();
 
-	if (tp_features.bright_acpimode) {
+	if (tp_features.bright_acpimode && acpi_video_backlight_support()) {
 		printk(TPACPI_INFO
 		       "This ThinkPad has standard ACPI backlight "
 		       "brightness control, supported by the ACPI "