hello-mod/hello.c: convert printk to pr_xxx

Convert to the newer pr_xxx aliases for logging, which embed the log level in
the macro names.

(From OE-Core rev: be119ead6d5bb01a50f78fd34024ded1289c9fd7)

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-skeleton/recipes-kernel/hello-mod/files/hello.c

@@ -21,13 +21,13 @@
 
 static int __init hello_init(void)
 {
-	printk("Hello World!\n");
+	pr_info("Hello World!\n");
 	return 0;
 }
 
 static void __exit hello_exit(void)
 {
-	printk("Goodbye Cruel World!\n");
+	pr_info("Goodbye Cruel World!\n");
 }
 
 module_init(hello_init);