8748 loader: ptblread() is broken with >512B sectors

Reviewed by: Robert Mustacchi <rm@joyent.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

usr/src/boot/sys/boot/common/disk.c

@@ -86,6 +86,12 @@ ptblread(void *d, void *buf, size_t blocks, uint64_t offset)
 	dev = (struct disk_devdesc *)d;
 	od = (struct open_disk *)dev->d_opendata;
 
+	/*
+	 * The strategy function assumes the offset is in units of 512 byte
+	 * sectors. For larger sector sizes, we need to adjust the offset to
+	 * match the actual sector size.
+	 */
+	offset *= (od->sectorsize / 512);
 	/*
 	 * As the GPT backup partition is located at the end of the disk,
 	 * to avoid reading past disk end, flag bcache not to use RA.