firewire: convert to idr_alloc()

Convert to the much saner new idr interface.

v2: Stefan pointed out that add_client_resource() may be called from
    non-process context.  Preload iff @gfp_mask contains __GFP_WAIT.
    Also updated to include minor upper limit check.

[tim.gardner@canonical.com: fix accidentally orphaned 'minor'[
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>