The Melfas MMS136 is similar to the other MMS variants but
has event packages of 6 bytes rather than 8 as the others.

The define is named FINGER_EVENT_SZ in the vendor drivers
so I renamed it from MMS*_PACKET_SZ to MMS*_EVENT_SZ.

After this patch, the touchscreen on the Samsung GT-I8530
works fine with PostmarketOS.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210404232619.3092682-1-linus.walleij@linaro.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>