fs/fscache: convert printk to pr_foo()

All printk converted to pr_foo() except internal.h: printk(KERN_DEBUG

Coalesce formats.

Add pr_fmt

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>