lavu/arm: Check for have_vfp_vm instead of !have_vfpv3 for float_dsp_vfp

This was missed in e754c8e8 / e2710e79 since those functions
weren't exercised by checkasm.

Fixes ticket #6766.

libavutil/arm/float_dsp_init_vfp.c

@@ -36,11 +36,11 @@ void ff_butterflies_float_vfp(float *av_restrict v1, float *av_restrict v2, int
 
 av_cold void ff_float_dsp_init_vfp(AVFloatDSPContext *fdsp, int cpu_flags)
 {
-    if (!have_vfpv3(cpu_flags)) {
+    if (have_vfp_vm(cpu_flags)) {
         fdsp->vector_fmul = ff_vector_fmul_vfp;
         fdsp->vector_fmul_window = ff_vector_fmul_window_vfp;
     }
     fdsp->vector_fmul_reverse = ff_vector_fmul_reverse_vfp;
-    if (!have_vfpv3(cpu_flags))
+    if (have_vfp_vm(cpu_flags))
         fdsp->butterflies_float = ff_butterflies_float_vfp;
 }