msm: venc: Set LTR info only when LTR is enabled

Set LTR use mask and mark index information to
firmware only when LTR count is non zero.

Change-Id: Icdcd0e8e29841e0cf4d2222ad3c2331aed2e3968
Signed-off-by: Darshana Patil <darshana@codeaurora.org>