Input: synaptics-rmi4 - fix crash when DPM query is not supported

Input: synaptics-rmi4 - fix crash when DPM query is not supported

Stop clobbering "item" variable when checking if the device supports
querying DPM values because its original value is still needed in
case when we need to fall back to the old way of figuring sensor size.

Reported-by: Richard Acayan <mailingradian@gmail.com>
Tested-by: Richard Acayan <mailingradian@gmail.com>
Fixes: 14d650fcb7fb ("Input: synaptics-rmi4 - add support for querying DPM value (F12)")
Link: https://lore.kernel.org/r/ZtdQW7nqAOEJDNBN@radian
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>