driver core: Release device_hotplug_lock when store_mem_state returns EINVAL

When inserting a wrong value to /sys/devices/system/memory/memoryX/state file,
following messages are shown. And device_hotplug_lock is never released.

================================================
[ BUG: lock held when returning to user space! ]
3.12.0-rc4-debug+ #3 Tainted: G        W
------------------------------------------------
bash/6442 is leaving the kernel with locks still held!
1 lock held by bash/6442:
 #0:  (device_hotplug_lock){+.+.+.}, at: [<ffffffff8146cbb5>] lock_device_hotplug_sysfs+0x15/0x50

This issue was introdued by commit fa2be40 (drivers: base: use standard
device online/offline for state change).

This patch releases device_hotplug_lcok when store_mem_state returns EINVAL.

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Reviewed-by: Toshi Kani <toshi.kani@hp.com>
CC: Seth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/memory.c

@@ -333,8 +333,10 @@ store_mem_state(struct device *dev,
 		online_type = ONLINE_KEEP;
 	else if (!strncmp(buf, "offline", min_t(int, count, 7)))
 		online_type = -1;
-	else
-		return -EINVAL;
+	else {
+		ret = -EINVAL;
+		goto err;
+	}
 
 	switch (online_type) {
 	case ONLINE_KERNEL:
@@ -357,6 +359,7 @@ store_mem_state(struct device *dev,
 		ret = -EINVAL; /* should never happen */
 	}
 
+err:
 	unlock_device_hotplug();
 
 	if (ret)