msm: vidc: fix failure to set LTR with index value

When MARKLTR/USELTR was set with a index value the value never
propagated to firmware resulting in failure to set the property.

Change-Id: I37536e1662c2d1092477fddde6838d4239805ac5
Signed-off-by: Ashray Kulkarni <ashrayk@codeaurora.org>