media: exynos4-is: Remove unused struct member input_index

This is no longer used since the conversion to DT

Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>