n_hdlc: put init/exit strings directly to prints

n_hdlc: put init/exit strings directly to prints

These strings were put aside from prints to save some bytes after module
load or when built-in -- they were freed after module load (__init ones) or
when the driver is selected as built-in (__exit ones).

The savings are negligible, but the code readability is worse by the
order of magnitude. So put the strings where they belong. Note that it
also used to make little sense putting const data in .data (the __exit
case).

While at it, switch to pr_info, pr_err, not using the KERN_INFO and _ERR
directly.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200219084118.26491-4-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>