Input: elants_i2c - fix division by zero if firmware reports zero phys size

Touchscreen firmware of ASUS Transformer TF700T reports zeros for the phys
size. Hence check whether the size is zero and don't set the resolution in
this case.

Reported-by: Jasper Korten <jja2000@gmail.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20210302100824.3423-1-digetx@gmail.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>