iwl4965: fix "TX Power requested while scanning"

Fix the following:

WARNING: at drivers/net/wireless/iwlegacy/iwl-4965.c:1128 \
iwl4965_send_tx_power+0x61/0x102 [iwl4965]() Hardware name: [...]
TX Power requested while scanning!

Pid: 5723, comm: kworker/u:28 Not tainted 2.6.39-0.rc4.4.fc14.x86_64 #1
Call Trace:
 [<ffffffff8104e27b>] warn_slowpath_common+0x85/0x9d
 [<ffffffffa02782e0>] ? iwl4965_show_temperature+0x49/0x49 [iwl4965]
 [<ffffffff8104e336>] warn_slowpath_fmt+0x46/0x48
 [<ffffffffa027712f>] iwl4965_send_tx_power+0x61/0x102 [iwl4965]
 [<ffffffff81477e05>] ? mutex_lock+0x36/0x50
 [<ffffffffa0278337>] iwl4965_bg_txpower_work+0x57/0x73 [iwl4965]
 [<ffffffff810647f3>] process_one_work+0x18d/0x286
 [<ffffffff81065a5e>] worker_thread+0xfd/0x181
 [<ffffffff81065961>] ? manage_workers.clone.16+0x172/0x172
 [<ffffffff81069036>] kthread+0x82/0x8a
 [<ffffffff81480524>] kernel_thread_helper+0x4/0x10
 [<ffffffff81068fb4>] ? kthread_worker_fn+0x14b/0x14b
 [<ffffffff81480520>] ? gs_change+0x13/0x13

Reported-and-tested-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>