rpc_pipefs: Replace one label in bl_resolve_deviceid()

The kfree() function was called in one case by
the bl_resolve_deviceid() function during error handling
even if the passed data structure member contained a null pointer.
This issue was detected by using the Coccinelle software.

Thus use an other label.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>