xen: xenbus: use put_device() instead of kfree()

[ Upstream commit 351b2bccede1cb673ec7957b35ea997ea24c8884 ]

Never directly free @dev after calling device_register(), even
if it returned an error! Always use put_device() to give up the
reference initialized.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>