hfsplus: convert tree_lock to mutex

tree_lock is used as mutex so make it a mutex.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Christoph Hellwig <hch@tuxera.com>

diff --cc fs/hfsplus/bfind.c
Simple merge

diff --cc fs/hfsplus/btree.c
Simple merge

diff --cc fs/hfsplus/hfsplus_fs.h
Simple merge