qemu-io's do_co_pwrite_zeroes is reinventing the coroutine wrapper
blk_pwrite_zeroes.  Just use the real thing directly.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221215130225.476477-1-pbonzini@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>