avfilter: add missing build deps to msad filter

Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -3910,6 +3910,7 @@ mpdecimate_filter_deps="gpl"
 mpdecimate_filter_select="pixelutils"
 minterpolate_filter_select="scene_sad"
 mptestsrc_filter_deps="gpl"
+msad_filter_select="scene_sad"
 negate_filter_deps="lut_filter"
 nlmeans_opencl_filter_deps="opencl"
 nlmeans_vulkan_filter_deps="vulkan spirv_compiler"

libavfilter/Makefile

@@ -394,6 +394,7 @@ OBJS-$(CONFIG_MIX_FILTER)                    += vf_mix.o framesync.o
 OBJS-$(CONFIG_MONOCHROME_FILTER)             += vf_monochrome.o
 OBJS-$(CONFIG_MORPHO_FILTER)                 += vf_morpho.o framesync.o
 OBJS-$(CONFIG_MPDECIMATE_FILTER)             += vf_mpdecimate.o
+OBJS-$(CONFIG_MSAD_FILTER)                   += vf_identity.o framesync.o
 OBJS-$(CONFIG_MULTIPLY_FILTER)               += vf_multiply.o framesync.o
 OBJS-$(CONFIG_NEGATE_FILTER)                 += vf_negate.o
 OBJS-$(CONFIG_NLMEANS_FILTER)                += vf_nlmeans.o