mgr/cephadm: reformat ceph.deployment.service_spec import line

mgr/cephadm: reformat ceph.deployment.service_spec import line

Quoting https://peps.python.org/pep-0008/#maximum-line-length
```
The preferred way of wrapping long lines is by using Python’s
implied line continuation inside parentheses, brackets and braces. Long
lines can be broken over multiple lines by wrapping expressions in
parentheses. These should be used in preference to using a backslash for
line continuation.
```

I also think it is much more readable and is similar to the style
applied by automated code formatting tools like `black`.

Signed-off-by: John Mulligan <jmulligan@redhat.com>
(cherry picked from commit 3d7b9342383ab5d4a2c7a346d6982aea09ebc6f8)