lockdep: Convert some users to const

These users of lockdep_is_held() either wanted lockdep_is_held to
take a const pointer, or would benefit from providing a const pointer.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: "David S. Miller" <davem@davemloft.net>
Link: https://lkml.kernel.org/r/20180117151414.23686-4-willy@infradead.org