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: NStephen Boyd <swboyd@chromium.org>
Signed-off-by: NDouglas Anderson <dianders@chromium.org>
Reviewed-by: NStephen Boyd <swboyd@chromium.org>
Signed-off-by: NSrinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210611083348.20170-9-srinivas.kandagatla@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -1606,7 +1606,7 @@ int nvmem_cell_read_u64(struct device *dev, const char *cell_id, u64 *val)
 }
 EXPORT_SYMBOL_GPL(nvmem_cell_read_u64);
 
-static void *nvmem_cell_read_variable_common(struct device *dev,
+static const void *nvmem_cell_read_variable_common(struct device *dev,
 						   const char *cell_id,
 						   size_t max_len, size_t *len)
 {
@@ -1652,7 +1652,7 @@ int nvmem_cell_read_variable_le_u32(struct device *dev, const char *cell_id,
 				    u32 *val)
 {
 	size_t len;
-	u8 *buf;
+	const u8 *buf;
 	int i;
 
 	buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len);
@@ -1683,7 +1683,7 @@ int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id,
 				    u64 *val)
 {
 	size_t len;
-	u8 *buf;
+	const u8 *buf;
 	int i;
 
 	buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len);