block: remove dead check

options must be non-NULL here, because a NULL value is replaced with
qdict_new earlier in the function.  Reported by Coverity.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
