toshiba_acpi: fix and cleanup toshiba_kbd_bl_mode_store()

The current code just returns -EINVAL because mode can't be equal to
both 1 and 2.

Also this function is messy so I have cleaned it up:
1) Remove initializers like "int time = -1".  Initializing variables to
   garbage values turns off GCC's uninitialized variable warnings so it
   can lead to bugs.
2) Use kstrtoint() instead of sscanf().
3) Use SCI_KBD_MODE_FNZ and SCI_KBD_MODE_AUTO instead of magic numbers 1
   and 2.
4) Don't check for "mode == -1" because that can't happen.
5) Preserve the error code from toshiba_kbd_illum_status_set().

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>