msm: mdss: Do not attempt to request TE irq again if already requested

If the TE irq is alredy requested and registred with a GPIO, then
setting it to true and not continuing with further requesting of
the same.

Change-Id: Iacd1677127c2663d88826e58f1b72704b58db939
Signed-off-by: Rashi Bindra <rbindra@codeaurora.org>