nvmem: core: fix regression in of_nvmem_cell_get()

NVMEM DT support seems to be totally broken after
commit e888d445ac33 ("nvmem: resolve cells from DT at registration time")
Fix this!

Index used in of_nvmem_cell_get() to find cell is specific to
consumer, It can not be used for searching the cell in provider.
Use device_node instead of this to find the matching cell in device
tree case.

Fixes: e888d445ac33 ("nvmem: resolve cells from DT at registration time")
Reported-by: Niklas Cassel <[e-mail]>
Signed-off-by: Srinivas Kandagatla <[e-mail]>
Tested-by: Niklas Cassel <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/nvmem/core.c

···
 	int			bytes;
 	int			bit_offset;
 	int			nbits;
+	struct device_node	*np;
 	struct nvmem_device	*nvmem;
 	struct list_head	node;
 };
···
 	mutex_lock(&nvmem_mutex);
 	list_del(&cell->node);
 	mutex_unlock(&nvmem_mutex);
+	of_node_put(cell->np);
 	kfree(cell->name);
 	kfree(cell);
 }
···
 			return -ENOMEM;
 
 		cell->nvmem = nvmem;
+		cell->np = of_node_get(child);
 		cell->offset = be32_to_cpup(addr++);
 		cell->bytes = be32_to_cpup(addr);
 		cell->name = kasprintf(GFP_KERNEL, "%pOFn", child);
···
 
 #if IS_ENABLED(CONFIG_OF)
 static struct nvmem_cell *
-nvmem_find_cell_by_index(struct nvmem_device *nvmem, int index)
+nvmem_find_cell_by_node(struct nvmem_device *nvmem, struct device_node *np)
 {
 	struct nvmem_cell *cell = NULL;
-	int i = 0;
 
 	mutex_lock(&nvmem_mutex);
 	list_for_each_entry(cell, &nvmem->cells, node) {
-		if (index == i++)
+		if (np == cell->np)
 			break;
 	}
 	mutex_unlock(&nvmem_mutex);
···
 	if (IS_ERR(nvmem))
 		return ERR_CAST(nvmem);
 
-	cell = nvmem_find_cell_by_index(nvmem, index);
+	cell = nvmem_find_cell_by_node(nvmem, cell_np);
 	if (!cell) {
 		__nvmem_device_put(nvmem);
 		return ERR_PTR(-ENOENT);