nvmem: rmem: Fix return value check in rmem_read()

In case of error, the function memremap() returns NULL pointer
not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.

Fixes: 5a3fa75 ("nvmem: Add driver to expose reserved memory as nvmem")
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20221118063840.6357-3-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Wei Yongjun

drivers/nvmem/rmem.c

@@ -37,9 +37,9 @@ static int rmem_read(void *context, unsigned int offset,
 	 * but as of Dec 2020 this isn't possible on arm64.
 	 */
 	addr = memremap(priv->mem->base, available, MEMREMAP_WB);
-	if (IS_ERR(addr)) {
+	if (!addr) {
 		dev_err(priv->dev, "Failed to remap memory region\n");
-		return PTR_ERR(addr);
+		return -ENOMEM;
 	}
 
 	count = memory_read_from_buffer(val, bytes, &off, addr, available);