mmc: debugfs: remove BUG_ON from mmc_ext_csd_open

Return error value for file_operations callback instead
of triggering BUG_ON which is meaningless. Personally I
don't believe n != EXT_CSD_STR_LEN could happen. Anyway,
propagate the error to the caller.

Signed-off-by: Shawn Lin <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/mmc/core/debugfs.c

···
 	for (i = 0; i < 512; i++)
 		n += sprintf(buf + n, "%02x", ext_csd[i]);
 	n += sprintf(buf + n, "\n");
-	BUG_ON(n != EXT_CSD_STR_LEN);
+
+	if (n != EXT_CSD_STR_LEN) {
+		err = -EINVAL;
+		goto out_free;
+	}
 
 	filp->private_data = buf;
 	kfree(ext_csd);