qcow2: remove incorrect coroutine_fn annotations

qcow2: remove incorrect coroutine_fn annotations

This is incorrect because qcow2_mark_clean() calls qcow2_flush_caches().
qcow2_mark_clean() is called from non-coroutine context in
qcow2_inactivate() and qcow2_amend_options().

Reviewed-by: Alberto Faria <afaria@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220922084924.201610-4-pbonzini@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>