eina: use matrix compose in place of equivalent code in matrix multiply

eina: use matrix compose in place of equivalent code in matrix multiply

Summary:
The eina_matrix3_compose and eina_matrix3_multiply API's are
mathematically identical (even though the implementations are
reversed... weird), except that the latter also includes a fastpath for
identity matrices.

Having two functionally equivalent APIs is redundant, so ideally one or
the other would be dropped.  But in order avoid API breakage, just have
one routine wrapper the other and eliminate the internal redundancy.

(Note that the parameter signatures of the two routines are different -
eina_matrix3_compose() takes the two input matrices first, and the
output matrix last, while eina_matrix3_multiply() takes the parameters
in the reverse order.  This inconsistency in the API style could result
in accidentally erroneous usage and would be an argument for deprecation
of one of the two APIs.)

Signed-off-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewers: cedric

Reviewed By: cedric

Differential Revision: https://phab.enlightenment.org/D5806

Signed-off-by: Cedric Bail <cedric@osg.samsung.com>