avcodec/x86/imdct36: fix building with nasm 2.11.05

fixes `operation size not specified` errors as described here:
http://stackoverflow.com/questions/36854583/compiling-ffmpeg-for-kali-linux-2

I rebuilt again with yasm and made sure it didn't break that.
Signed-off-by: NMichael Niedermayer <michael@niedermayer.cc>

libavcodec/x86/imdct36.asm

@@ -145,9 +145,9 @@ SECTION .text
 %macro STORE 4
 %if cpuflag(sse4)
     movss     [%3       ], %1
-    extractps [%3 +   %4], %1, 1
-    extractps [%3 + 2*%4], %1, 2
-    extractps [%3 + 3*%4], %1, 3
+    extractps dword [%3 +   %4], %1, 1
+    extractps dword [%3 + 2*%4], %1, 2
+    extractps dword [%3 + 3*%4], %1, 3
 %else
     movhlps %2, %1
     movss   [%3       ], %1