powerpc/perf/24x7: Fix lockdep warning

The sysfs attributes for the 24x7 counters are dynamically allocated.
Initialize the attributes using sysfs_attr_init() to fix following
warning which occurs when CONFIG_DEBUG_LOCK_VMALLOC=y.

[    0.346249] audit: initializing netlink subsys (disabled)
[    0.346284] audit: type=2000 audit(1436295254.340:1): initialized
[    0.346489] BUG: key c0000000efe90198 not in .data!
[    0.346491] DEBUG_LOCKS_WARN_ON(1)
[    0.346502] ------------[ cut here ]------------
[    0.346504] WARNING: at ../kernel/locking/lockdep.c:3002
[    0.346506] Modules linked in:
Reported-by: Gustavo Luiz Duarte <gustavold@linux.vnet.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Tested-by: Gustavo Luiz Duarte <gustavold@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/perf/hv-24x7.c

@@ -320,6 +320,8 @@ static struct attribute *device_str_attr_create_(char *name, char *str)
 	if (!attr)
 		return NULL;
 
+	sysfs_attr_init(&attr->attr.attr);
+
 	attr->var = str;
 	attr->attr.attr.name = name;
 	attr->attr.attr.mode = 0444;