nvmem: core: validate nvmem config before parsing

nvmem provider has to provide either reg_read/write, add a check
to enforce this.

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200310132257.23358-9-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/core.c

@@ -339,6 +339,9 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
 	if (!config->dev)
 		return ERR_PTR(-EINVAL);
 
+	if (!config->reg_read && !config->reg_write)
+		return ERR_PTR(-EINVAL);
+
 	nvmem = kzalloc(sizeof(*nvmem), GFP_KERNEL);
 	if (!nvmem)
 		return ERR_PTR(-ENOMEM);