gst/base/gstbasetransform.c: Small cleanups.

gst/base/gstbasetransform.c: Small cleanups.

Original commit message from CVS:
* gst/base/gstbasetransform.c:
(gst_base_transform_prepare_output_buf),
(gst_base_transform_handle_buffer):
Small cleanups.
If we're processing a buffer and need to allocate an output
buffer, we cannot accept a format change. If we did get a
format change, we have to alloc a buffer ourselves of the
right size.