codecs: h265decoder: Fix a typo of NumPocTotalCurr when process ref pic list.

codecs: h265decoder: Fix a typo of NumPocTotalCurr when process ref pic list.

We should use the NumPocTotalCurr value stored in decoder, which is a calculated
valid value, rather than use the invalid value in the slice header. Most of the
time, the NumPocTotalCurr is 0 and make the tmp_refs a very short length, and
causes the decoder's wrong result.
By the way, the NumPocTotalCurr is not the correct name specified in H265 spec,
its name should be NumPicTotalCurr. We change it to the correct name.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/2414>