target/iblock: Use match_strlcpy for Opt_udev_path string assignment

Following commit dbc6e022 from Al Viro for fileio, go ahead and make
Opt_udev_path within iblock_set_configfs_dev_params use match_strlcpy
instead of the match_strdup -> snprintf -> kfree equivalent.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>