staging: lustre: Remove typedef and update cfs_hash_bucket struct

Remove typedef keyword and rename the cfs_hash_bucket_t struct to
cfs_hash_bucket in libcfs_hash.h. These changes resolve the
"Do not add new typedefs" warning generated by checkpatch.pl and
meet kernel coding style.

The struct variables in hash.c are updated to reflect this change
as well.

Signed-off-by: Lisa Nguyen <lisa@xenapiadmin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>