s390/dasd: Move duplicate code to separate function

For storing retrieved path information both the if and else block in
dasd_eckd_read_conf() use the same code. To avoid duplicate code this
should be done after the if/else block. To further increase readability,
move the code to a new function, dasd_eckd_store_conf_data().

Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>