avcodec/x86/pngdsp: add missing emms at the end of add_png_paeth_prediction

Fixes unpredictable behavior with floats.

Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit 57a29f2e7dd2374a1df27316c6cf7c0225e86758)

libavcodec/x86/pngdsp.asm

@@ -151,6 +151,7 @@ cglobal add_png_paeth_prediction, 5, 7, %1, dst, src, top, w, bpp, end, cntr
     dec              cntrq
     jge .bpp_loop
     POP               dstq
+    emms
     RET
 %endmacro