i386/cpu: Mark avx10_version filtered when prefix is NULL

i386/cpu: Mark avx10_version filtered when prefix is NULL

In x86_cpu_filter_features(), if host doesn't support AVX10, the
configured avx10_version should be marked as filtered regardless of
whether prefix is NULL or not.

Check prefix before warn_report() instead of checking for
have_filtered_features.

Cc: qemu-stable@nongnu.org
Fixes: commit bccfb846fd52 ("target/i386: add AVX10 feature and AVX10 version property")
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Tao Su <tao1.su@linux.intel.com>
Link: https://lore.kernel.org/r/20241106030728.553238-2-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>