Add comment why the code has been disabled.

Requested by:	rpaulo

sys/boot/common/part.c

@@ -372,7 +372,7 @@ ptable_ebrread(struct ptable *table, void *dev, diskread_t dread)
 	if (buf == NULL)
 		return (table);
 	for (i = 0; i < MAXEBRENTRIES; i++) {
-#if 0
+#if 0	/* Some BIOSes return an incorrect number of sectors */
 		if (offset >= table->sectors)
 			break;
 #endif
@@ -665,7 +665,7 @@ ptable_open(void *dev, off_t sectors, uint16_t sectorsize,
 		end = le32toh(dp[i].dp_size);
 		if (start == 0 || end == 0)
 			continue;
-#if 0
+#if 0	/* Some BIOSes return an incorrect number of sectors */
 		if (start + end - 1 >= sectors)
 			continue;	/* XXX: ignore */
 #endif