core_ctl: use pr_fmt

We use pr_* to print info/warn/error messages. Use pr_fmt so
that the messages are prefixed by "core_ctl:" string.

Change-Id: Icc84db30ebf0855599431366d090a2b1c94da6d0
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>