Input: edt-ft5x06 - use get_unaligned_be16()

Instead of doing conversion by hand, let's use the proper accessors.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Tested-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>