samples/kretprobe: convert the printk to pr_info/pr_err

samples/kretprobe: convert the printk to pr_info/pr_err

We prefer to use the pr_* to print out the log now, this patch converts
the printk to pr_info.  In the error path, use the pr_err to replace the
printk.

Link: http://lkml.kernel.org/r/1464143083-3877-3-git-send-email-shijie.huang@arm.com
Signed-off-by: Huang Shijie <shijie.huang@arm.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steve Capper <steve.capper@arm.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>