nine: fix write into array in TEXM3x3

Fix warning:
nine_shader.c:2134:9: warning: array index 4 is past the
end of the array (which contains 4 elements) [-Warray-bounds]

No visible changes.

Signed-off-by: David Heidelberger <david.heidelberger@ixit.cz>
Signed-off-by: Tiziano Bacocco <tizbac2@gmail.com>