input: touchscreen: maxim_sti: remove SPI data swap in byte

SPI bus driver did data swap to address big-little endian conversion.
However, recent change in bus driver removes this conversion to align
with hardware peripheral design. Therefore, touchscreen driver sets
SPI bits per word to 16 in order to achieve best data transfer
performance and remove this swap.

Change-Id: Id24417e5afe055315b4c173961509aa7d6806034
Signed-off-by: Chun Zhang <chunz@codeaurora.org>