dm: mmc: Check that drivers have operations

When binding a new MMC device, make sure that it has the required
operations. Since for now we still support *not* having the operations
(with CONFIG_DM_MMC_OPS not enabled) it makes sense to add this check.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mmc/mmc-uclass.c b/drivers/mmc/mmc-uclass.c
index 8d03ec6..c9b6364 100644
--- a/drivers/mmc/mmc-uclass.c
+++ b/drivers/mmc/mmc-uclass.c
@@ -196,6 +196,10 @@
 	struct udevice *bdev;
 	int ret, devnum = -1;
 
+#ifdef CONFIG_DM_MMC_OPS
+	if (!mmc_get_ops(dev))
+		return -ENOSYS;
+#endif
 #ifndef CONFIG_SPL_BUILD
 	/* Use the fixed index with aliase node's index */
 	fdtdec_get_alias_seq(gd->fdt_blob, "mmc", dev_of_offset(dev), &devnum);