Bluetooth: Remove useless flush_work() causing lockdep warnings

The calls to flush_work() are pointless in a single thread workqueue
and they are actually causing a lockdep warning.

=============================================
[ INFO: possible recursive locking detected ]
2.6.30-rc6-02911-gbb803cf #16
---------------------------------------------
bluetooth/2518 is trying to acquire lock:
 (bluetooth){+.+.+.}, at: [<c0130c14>] flush_work+0x28/0xb0

but task is already holding lock:
 (bluetooth){+.+.+.}, at: [<c0130424>] worker_thread+0x149/0x25e

other info that might help us debug this:
2 locks held by bluetooth/2518:
 #0:  (bluetooth){+.+.+.}, at: [<c0130424>] worker_thread+0x149/0x25e
 #1:  (&conn->work_del){+.+...}, at: [<c0130424>] worker_thread+0x149/0x25e

stack backtrace:
Pid: 2518, comm: bluetooth Not tainted 2.6.30-rc6-02911-gbb803cf #16
Call Trace:
 [<c03d64d9>] ? printk+0xf/0x11
 [<c0140d96>] __lock_acquire+0x7ce/0xb1b
 [<c0141173>] lock_acquire+0x90/0xad
 [<c0130c14>] ? flush_work+0x28/0xb0
 [<c0130c2e>] flush_work+0x42/0xb0
 [<c0130c14>] ? flush_work+0x28/0xb0
 [<f8b84966>] del_conn+0x1c/0x84 [bluetooth]
 [<c0130469>] worker_thread+0x18e/0x25e
 [<c0130424>] ? worker_thread+0x149/0x25e
 [<f8b8494a>] ? del_conn+0x0/0x84 [bluetooth]
 [<c0133843>] ? autoremove_wake_function+0x0/0x33
 [<c01302db>] ? worker_thread+0x0/0x25e
 [<c013355a>] kthread+0x45/0x6b
 [<c0133515>] ? kthread+0x0/0x6b
 [<c01034a7>] kernel_thread_helper+0x7/0x10

Based on a report by Oliver Hartkopp <oliver@hartkopp.net>

Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Tested-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>