media: exynos4-is: Use global num_sensors rather than local index

Instead of keeping a local copy of how many sensors we've probed
(which may not even properly represent the number of sensors
probed if we have a port without a sensor), use the global
num_sensors counter that has the actual number used.

This will also make it easier to add support for multiple sensors
being connected to the same port.

Signed-off-by: Jonathan Bakker <xc-racer2@live.ca>
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>