input: atmel_mxt_ts: Synchronous PM request starting Secure Touch

Maintain I2C adapter clocks on when starting Secure Touch
using the synchronous version of pm_runtime_get.

Change-Id: Ie30ea56af9e045239099652124740565428518f8
Acked-by: Christian Bolis <cbolis@qti.qualcomm.com>
Signed-off-by: Keith Fallows <keithf@codeaurora.org>