lockdep: make MAX_LOCKDEP_SUBCLASSES unconditionally visible

This define is needed by i2c_adapter_depth() to detect if we don't
exceed the maximum number of lock subclasses. Make it visible even
if lockdep is disabled.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Peter Rosin <peda@axentia.se>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>