When configure has been run with --with-pkgversion=xyz, the shell complains
about a missing ']' in this script.

Fixes: 2c273f32 ("meson: generate qemu-version.h")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>