sws: fix typo in xyz2rgb matrix use.

Found-by: ubitux
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/swscale.c

@@ -823,7 +823,7 @@ static void xyz12Torgb48(struct SwsContext *c, uint16_t *dst,
                 c->xyz2rgb_matrix[1][1] * y +
                 c->xyz2rgb_matrix[1][2] * z >> 12;
             b = c->xyz2rgb_matrix[2][0] * x +
-                c->xyz2rgb_matrix[1][2] * y +
+                c->xyz2rgb_matrix[2][1] * y +
                 c->xyz2rgb_matrix[2][2] * z >> 12;
 
             // limit values to 12-bit depth

tests/ref/fate/jpeg2000-dcinema

 #tb 0: 1/24
-0,          0,          0,        1, 12441600, 0x05a68cf7
-0,          1,          1,        1, 12441600, 0x43788893
+0,          0,          0,        1, 12441600, 0x380d805a
+0,          1,          1,        1, 12441600, 0xfde5a60a