tcmu: Fix dev_config_store

Currently when there is a reconfig, the uio_info->name
does not get updated to reflect the change in the dev_config
name change.

On restart tcmu-runner there will be a mismatch between
the dev_config string in uio and the tcmu structure that contains
the string. When this occurs it'll reload the one in uio
and you lose the reconfigured device path.

v2: Created a helper function for the updating of uio_info

Signed-off-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>