kldxref: Simplify elf_read_raw_data

Use pread as a valid offset is always passed now.  Originally the DSO
code read the .hash section in two separate requests and relied on the
implicit offset for the second read, but now the hash table is fetched
in a single call.

Reviewed by:	imp
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D43125

usr.sbin/kldxref/elf.c

@@ -204,11 +204,7 @@ elf_read_raw_data(struct elf_file *efile, off_t offset, void *dst, size_t len)
 {
 	ssize_t nread;
 
-	if (offset != (off_t)-1) {
-		if (lseek(efile->ef_fd, offset, SEEK_SET) == -1)
-			return (EIO);
-	}
-	nread = read(efile->ef_fd, dst, len);
+	nread = pread(efile->ef_fd, dst, len, offset);
 	if (nread == -1)
 		return (errno);
 	if (nread != len)