Input: usbtouchscreen - fix buffer overflow, make more egalax work

Fix a buffer overflow in mutli-packet handling code.  The overflow can
only happen with eGalax devices and is even there very unlikely (only
non-report packet are affected any only when truncated after the first
byte).

Also changes the mutli-packet handling code not to drop unknown packets,
but rather just drop one byte.  This allows synchronizing on report packets
in the data stream.  It's required for some egalax devices to work at all.

Also remove the pointless 'flags' member of the device struct and set the
version number to 0.6, plus some minor cleanups.

[akpm@linux-foundation.org: coding-style fixes]

Signed-off-by: Daniel Ritz <daniel.ritz@gmx.ch>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>