package/libmatroska: bump to version 1.6.2

package/libmatroska: bump to version 1.6.2

Extract from ChangeLog:
 - In release 1.6.1 the version number in CMakeLists.txt wasn't
   updated, affecting the installed cmake and pkgconfig files. The
   version number has been bumped to 1.6.2 in all relevant files now.
 - "KaxBlockAddIDValue" class: this class is no longer marked as
   "mandatory" in order to coincide with the latest specification.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>