dsputil: add missing HAVE_YASM guard

Fix compile error under
"--disable-optimizations --disable-yasm --disable-inline-asm"
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/x86/dsputil_mmx.c

@@ -82,6 +82,7 @@ DECLARE_ALIGNED(16, const double, ff_pd_1)[2] = { 1.0, 1.0 };
 DECLARE_ALIGNED(16, const double, ff_pd_2)[2] = { 2.0, 2.0 };
 
 
+#if HAVE_YASM
 void ff_put_pixels8_x2_mmxext(uint8_t *block, const uint8_t *pixels,
                               int line_size, int h);
 void ff_put_pixels8_x2_3dnow(uint8_t *block, const uint8_t *pixels,
@@ -180,6 +181,7 @@ void ff_put_no_rnd_mpeg4_qpel8_v_lowpass_mmxext(uint8_t *dst, uint8_t *src,
                                                 int dstStride, int srcStride);
 #define ff_put_no_rnd_pixels16_mmxext ff_put_pixels16_mmxext
 #define ff_put_no_rnd_pixels8_mmxext ff_put_pixels8_mmxext
+#endif /* HAVE_YASM */
 
 
 #if HAVE_INLINE_ASM