avcodec/faandct: use typedef instead of #define

See e.g https://stackoverflow.com/questions/1666353/are-typedef-and-define-the-same-in-c
for rationale.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

libavcodec/faandct.c

@@ -29,7 +29,7 @@
 #include "libavutil/internal.h"
 #include "libavutil/libm.h"
 
-#define FLOAT float
+typedef float FLOAT;
 
 /* numbers generated by arbitrary precision arithmetic followed by truncation
 to 36 fractional digits (enough for a 128-bit IEEE quad, see /usr/include/math.h