vfi/x86/vf_idet: fix incorrect use of paddq

paddq is an SSE2 instruction so it cannot be used for MMX.

This was probably just a typo because the sums are dwords anyway.
Reviewed-by: Pascal Massimino <pascal.massimino@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/x86/vf_idet.asm

@@ -73,7 +73,7 @@ cglobal idet_filter_line, 4, 5, 0, a, b, c, width, index
 
     mova      m0, m_sum
     psrlq     m_sum, 0x20
-    paddq     m0, m_sum
+    paddd     m0, m_sum
     movd      eax, m0
     RET
 %endmacro