Input: synaptics-rmi4 - set reduced reporting mode only when requested

Input: synaptics-rmi4 - set reduced reporting mode only when requested

The previous patch "c5ccf2ad3d33 (Input: synaptics-rmi4 - switch to
reduced reporting mode)" enabled reduced reporting mode unintentionally
on some devices, if the firmware was configured with default Delta X/Y
threshold values. The result unintentionally degrade the performance of
some touchpads.

This patch checks to see that the driver is modifying the delta X/Y
thresholds before modifying the reporting mode.

Signed-off-by: Andrew Duggan <aduggan@synaptics.com>
Fixes: c5ccf2ad3d33 ("Input: synaptics-rmi4 - switch to reduced reporting mode")
Link: https://lore.kernel.org/r/20200312005549.29922-1-aduggan@synaptics.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>