video/converter: increase the number of cache lines for resampling

video/converter: increase the number of cache lines for resampling

The exising hardcoded max default does not account for the possible
-1 offset when retrieving lines for resampling.  As a result, when
another chain has the same number of cache lines (4), the resample
operation would be attempting to generate 5 lines with a cache size
of 4 and would overwrite the first cache line.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/issues/821

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/-/merge_requests/938>