dt-bindings: mmc: update mmc-card.yaml reference

The recent change ("dt-bindings: mmc: Convert MMC Card binding to a schema")
renamed: Documentation/devicetree/bindings/mmc/mmc-card.txt
to: Documentation/devicetree/bindings/mmc/mmc-card.yaml.

Let's update its cross-reference accordingly.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/820bb7a1d7e0e51cbea72c9bee6bce806427d1f3.1631785820.git.mchehab+huawei@kernel.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/omap_hsmmc.c

@@ -1510,7 +1510,7 @@ static void omap_hsmmc_init_card(struct mmc_host *mmc, struct mmc_card *card)
 		 * REVISIT: should be moved to sdio core and made more
 		 * general e.g. by expanding the DT bindings of child nodes
 		 * to provide a mechanism to provide this information:
-		 * Documentation/devicetree/bindings/mmc/mmc-card.txt
+		 * Documentation/devicetree/bindings/mmc/mmc-card.yaml
 		 */
 
 		np = of_get_compatible_child(np, "ti,wl1251");