drm/msm/dsi-staging: fix spurious irq status for TE signal

Currently in dsi driver relies on vsync gpio irq to periodically
check if panel is sending TE signal properly or not. But due to
lazy disabling of edge triggered irqs sometimes when driver enables
back the irq line, it might end up getting a previously pending
irq, which will give false indication of panel sending TE even if
at present panel has stopped sending TE signal. So do not perform
lazy disabling of TE irq.

Change-Id: Iabd9d76aad7d50003cd8af7810794b2e8ecbbbc2
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>