mtd: Fix the check on nvmem_register() ret code

Commit 20167b70 ("nvmem: use EOPNOTSUPP instead of ENOSYS") changed
the nvmem_register() ret code from ENOSYS to EOPNOTSUPP when
CONFIG_NVMEM is not enabled, but the check in mtd_nvmem_add() was not
adjusted accordingly.

Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Alban Bedel <albeu@free.fr>
Fixes: c4dfa25a ("mtd: add support for reading MTD devices via the nvmem API")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>
Reviewed-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>

drivers/mtd/mtdcore.c

@@ -522,7 +522,7 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
 	mtd->nvmem = nvmem_register(&config);
 	if (IS_ERR(mtd->nvmem)) {
 		/* Just ignore if there is no NVMEM support in the kernel */
-		if (PTR_ERR(mtd->nvmem) == -ENOSYS) {
+		if (PTR_ERR(mtd->nvmem) == -EOPNOTSUPP) {
 			mtd->nvmem = NULL;
 		} else {
 			dev_err(&mtd->dev, "Failed to register NVMEM device\n");