msm: mdss: Fix incorrect handle of vsync for SPI display

SPI can't report vsync event to user space correctly due to
incorrect count and unbalanced handling of the TE interrupt.

Change-Id: Ic0f46216e17c7f92c6d05a66653cfd98c0e775fb
Signed-off-by: Lei Chen <chenlei@codeaurora.org>
Signed-off-by: Raghavendra Ambadas <rambad@codeaurora.org>