Input: elantech - fix firmware version check

The check determining whether device should use 4- or 6-byte packets
was trying to compare firmware with 2.48, but was failing on majors
greater than 2. The new check ensures that versions like 4.1 are
checked properly.

Signed-off-by: Florian Ragwitz <rafl@debian.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>