input: msg21xx_ts: release touch when finger leaves the panel

When fingers on the panel decrease, release corresponding touches.

  This patch is propagated from 3.10 kernel
    commit: 24e3a5036d3ca72b409315e70629865c6184a02c

Change-Id: Iafc3a9dda252417fcd06e3d9d24fb73b4d6f8e58
Signed-off-by: Mao Li <maol@codeaurora.org>
Signed-off-by: Sudhakar Manapati <smanap@codeaurora.org>