generic: ar8216: remove an unblanced mutex_unlock call

Fixes the following warning:

[   94.080000]
[   94.080000] =====================================
[   94.080000] [ BUG: bad unlock balance detected! ]
[   94.080000] 3.3.8 #2 Tainted: G           O
[   94.080000] -------------------------------------
[   94.080000] swconfig/1220 is trying to release lock (&priv->mib_lock) at:
[   94.080000] [<801df8f4>] ar8216_sw_get_port_mib+0x138/0x16c
[   94.080000] but there are no more locks to release!
[   94.080000]
[   94.080000] other info that might help us debug this:
[   94.080000] 2 locks held by swconfig/1220:
[   94.080000]  #0:  (genl_mutex){+.+...}, at: [<80222430>] genl_rcv+0x14/0x34
[   94.080000]  #1:  (&dev->sw_mutex){+.+...}, at: [<801da018>] swconfig_get_dev+0x88/0xb4
[   94.080000]
[   94.080000] stack backtrace:
[   94.080000] Call Trace:
[   94.080000] [<8028dc58>] dump_stack+0x8/0x34
[   94.080000] [<800a5128>] print_unlock_inbalance_bug+0xe0/0xfc
[   94.080000] [<800a82c0>] lock_release+0x18c/0x1c8
[   94.080000] [<80292074>] __mutex_unlock_slowpath+0xd8/0x17c
[   94.080000] [<801df8f4>] ar8216_sw_get_port_mib+0x138/0x16c
[   94.080000] [<801db688>] swconfig_get_attr+0xbc/0x394
[   94.080000] [<8022261c>] genl_rcv_msg+0x1cc/0x214
[   94.080000] [<80221a18>] netlink_rcv_skb+0x6c/0xe8
[   94.080000] [<80222440>] genl_rcv+0x24/0x34
[   94.080000] [<80221370>] netlink_unicast+0x15c/0x22c
[   94.080000] [<8022175c>] netlink_sendmsg+0x240/0x2d0
[   94.080000] [<801ef544>] sock_sendmsg+0x84/0x9c
[   94.080000] [<801f0648>] __sys_sendmsg+0x1cc/0x270
[   94.080000] [<801f207c>] sys_sendmsg+0x48/0x7c
[   94.080000] [<8006ad78>] stack_done+0x20/0x40
[   94.080000]

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34282 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/generic/files/drivers/net/phy/ar8216.c

@@ -1549,7 +1549,6 @@ ar8216_sw_get_port_mib(struct switch_dev *dev,
 		goto unlock;
 
 	ar8216_mib_fetch_port_stat(priv, port, false);
-	mutex_unlock(&priv->mib_lock);
 
 	len += snprintf(buf + len, sizeof(priv->buf) - len,
 			"Port %d MIB counters\n",