acerhdf: Clean up includes

* The acerhdf driver isn't an ACPI driver, so it needs not include
  <acpi/acpi_drivers.h>. All it uses is ec_read() and ec_write(), for
  which <linux/acpi.h> is sufficient.
* I couldn't find any reason why <linux/fs.h> and <linux/sched.h> were
  included.

This should avoid unneeded rebuilds of the acerhdf driver.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Peter Feuerer <peter@piie.net>
Cc: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>