msm: vidc: Use EOS flag instead of FLAG_LAST

Using FLAG_LAST is creating problems in v4l2 ftamework
instead use EOS flag for indicating last frame.

CRs-Fixed: 2198690
Change-Id: Ia12ea8fbbe6494849d1ea14d1319d3e863b411eb
Signed-off-by: Vaibhav Deshu Venkatesh <vdeshuve@codeaurora.org>