wavparse: Actually clip to upstream size instead of size of the data chunk
wavparse: Actually clip to upstream size instead of size of the data chunk

There might be other chunks after the data chunk, so clipping the chunk
size with the data size can lead to a negative number and all following
calculations go wrong and cause crashes or worse.

This was introduced in 3ac119bbe2c360e28c087cf3852ea769d611b120.

https://bugzilla.gnome.org/show_bug.cgi?id=783760

stfl/gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good,stfl/gst-plugins-good