avcodec/ppc/fdctdsp: use more accurate constants

Whoever wrote this stuff had a pretty bad libm - digits differ pretty
quickly.
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

libavcodec/ppc/fdctdsp.c

@@ -37,13 +37,13 @@
 #define vu16(v) ((vector unsigned short) (v))
 #define vu32(v)   ((vector unsigned int) (v))
 
-#define C1     0.98078525066375732421875000 /* cos(1 * PI / 16) */
-#define C2     0.92387950420379638671875000 /* cos(2 * PI / 16) */
-#define C3     0.83146959543228149414062500 /* cos(3 * PI / 16) */
-#define C4     0.70710676908493041992187500 /* cos(4 * PI / 16) */
-#define C5     0.55557024478912353515625000 /* cos(5 * PI / 16) */
-#define C6     0.38268342614173889160156250 /* cos(6 * PI / 16) */
-#define C7     0.19509032368659973144531250 /* cos(7 * PI / 16) */
+#define C1     0.98078528040323044912618224 /* cos(1 * PI / 16) */
+#define C2     0.92387953251128675612818319 /* cos(2 * PI / 16) */
+#define C3     0.83146961230254523707878838 /* cos(3 * PI / 16) */
+#define C4     0.70710678118654752440084436 /* cos(4 * PI / 16) */
+#define C5     0.55557023301960222474283081 /* cos(5 * PI / 16) */
+#define C6     0.38268343236508977172845998 /* cos(6 * PI / 16) */
+#define C7     0.19509032201612826784828487 /* cos(7 * PI / 16) */
 
 #define W0 -(2 * C2)
 #define W1  (2 * C6)