toshiba_acpi: Fix regression caused by backlight extra check code

Bug 86521 uncovered that some TOS6208 devices also return
non zero values on a write call to the backlight method,
thus getting caught and bailed out by the extra check code.

This patch changes the set_lcd_brightness function to its
"original" state by just adapting it to the new function
format.

Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>