Mark conditionally used variable T2 as av_unused; avoids the warning:

libavutil/sha.c:183: warning: unused variable `T2'

Originally committed as revision 19551 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/sha.c

@@ -180,7 +180,7 @@ static void sha256_transform(uint32_t *state, const uint8_t buffer[64])
 {
     unsigned int i, a, b, c, d, e, f, g, h;
     uint32_t block[64];
-    uint32_t T1, T2;
+    uint32_t T1, av_unused(T2);
 
     a = state[0];
     b = state[1];