lib: dynamic_debug: use kbasename()

Remove the custom implementation of the functionality similar to kbasename().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>