Input: adxl34x - don't set THRESH_TAP twice

The datasheet doesn't say anything about writing twice, so this was
probably overlooked.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>