nvmem: core: constify nvmem_cell_read_variable_common() return value

The caller doesn't modify the memory pointed to by the pointer so it
can be const.

Suggested-by: Stephen Boyd <[e-mail]>
Signed-off-by: Douglas Anderson <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Signed-off-by: Srinivas Kandagatla <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/nvmem/core.c

···
 }
 EXPORT_SYMBOL_GPL(nvmem_cell_read_u64);
 
-static void *nvmem_cell_read_variable_common(struct device *dev,
-					     const char *cell_id,
-					     size_t max_len, size_t *len)
+static const void *nvmem_cell_read_variable_common(struct device *dev,
+						   const char *cell_id,
+						   size_t max_len, size_t *len)
 {
 	struct nvmem_cell *cell;
 	int nbits;
···
 				    u32 *val)
 {
 	size_t len;
-	u8 *buf;
+	const u8 *buf;
 	int i;
 
 	buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len);
···
 				    u64 *val)
 {
 	size_t len;
-	u8 *buf;
+	const u8 *buf;
 	int i;
 
 	buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len);