mmc: core: Normalize the error handling branch in sd_read_ext_regs()

Let's use pr_err() to output the error messages and let's extend a comment
to clarify why returning 0 (success) in one case make sense.

Fixes: c784f927 ("mmc: core: Read the SD function extension registers for power management")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[Ulf: Clarified the comment and the commit-msg]
Link: https://lore.kernel.org/r/20221130134920.2109-1-thunder.leizhen@huawei.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/sd.c

@@ -1259,7 +1259,7 @@ static int sd_read_ext_regs(struct mmc_card *card)
 	 */
 	err = sd_read_ext_reg(card, 0, 0, 0, 512, gen_info_buf);
 	if (err) {
-		pr_warn("%s: error %d reading general info of SD ext reg\n",
+		pr_err("%s: error %d reading general info of SD ext reg\n",
 			mmc_hostname(card->host), err);
 		goto out;
 	}
@@ -1273,7 +1273,12 @@ static int sd_read_ext_regs(struct mmc_card *card)
 	/* Number of extensions to be find. */
 	num_ext = gen_info_buf[4];
 
-	/* We support revision 0, but limit it to 512 bytes for simplicity. */
+	/*
+	 * We only support revision 0 and limit it to 512 bytes for simplicity.
+	 * No matter what, let's return zero to allow us to continue using the
+	 * card, even if we can't support the features from the SD function
+	 * extensions registers.
+	 */
 	if (rev != 0 || len > 512) {
 		pr_warn("%s: non-supported SD ext reg layout\n",
 			mmc_hostname(card->host));
@@ -1288,7 +1293,7 @@ static int sd_read_ext_regs(struct mmc_card *card)
 	for (i = 0; i < num_ext; i++) {
 		err = sd_parse_ext_reg(card, gen_info_buf, &next_ext_addr);
 		if (err) {
-			pr_warn("%s: error %d parsing SD ext reg\n",
+			pr_err("%s: error %d parsing SD ext reg\n",
 				mmc_hostname(card->host), err);
 			goto out;
 		}