rpmb: Remove some useless locking

There is no need for explicit locking when using the ida API, as stated in
the doc related to ida_alloc_range() / ida_free().

So remove rpmb_mutex.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/b1fcc6707ec2b6309d50060fa52ccc2c892afde2.1728507153.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/rpmb-core.c

@@ -13,7 +13,6 @@
 #include <linux/slab.h>
 
 static DEFINE_IDA(rpmb_ida);
-static DEFINE_MUTEX(rpmb_mutex);
 
 /**
  * rpmb_dev_get() - increase rpmb device ref counter
@@ -63,9 +62,7 @@ static void rpmb_dev_release(struct device *dev)
 {
 	struct rpmb_dev *rdev = to_rpmb_dev(dev);
 
-	mutex_lock(&rpmb_mutex);
 	ida_free(&rpmb_ida, rdev->id);
-	mutex_unlock(&rpmb_mutex);
 	kfree(rdev->descr.dev_id);
 	kfree(rdev);
 }
@@ -175,9 +172,7 @@ struct rpmb_dev *rpmb_dev_register(struct device *dev,
 		goto err_free_rdev;
 	}
 
-	mutex_lock(&rpmb_mutex);
 	ret = ida_alloc(&rpmb_ida, GFP_KERNEL);
-	mutex_unlock(&rpmb_mutex);
 	if (ret < 0)
 		goto err_free_dev_id;
 	rdev->id = ret;