gst/matroska/ebml-read.c: Don't create unnecessary sub-buffers all the time. Dramatically improves performance with m...

Original commit message from CVS:
Patch by: Jindrich Makovicka  <jindrich.makivicka at itonis tv>
* gst/matroska/ebml-read.c: (gst_ebml_read_peek_bytes),
(gst_ebml_read_pull_bytes), (gst_ebml_read_element_id),
(gst_ebml_read_element_length), (gst_ebml_read_buffer),
(gst_ebml_read_bytes), (gst_ebml_read_uint), (gst_ebml_read_sint),
(gst_ebml_read_float), (gst_ebml_read_ascii),
(gst_ebml_read_binary):
Don't create unnecessary sub-buffers all the time. Dramatically
improves performance with multiple concurrently running
matroskademux instances (#341818) (and avoids doing
unnecessarily inefficient things in the general case).