perf annotate: Fix SEGV with assembly labels

I'm getting a SEGV when running perf annotate on a ppc64 box. The objdump -S output causing the SEGV looks like:

b .ret_from_except_lite
c00000000000a508: b c00000000000a4d4 <.ret_from_except_lite>

1: bl .save_nvgprs
c00000000000a50c: bl c00000000000a110 <.save_nvgprs>

symbol__parse_objdump_line makes an effort to distinguish between instruction addresses and assembly labels but the check is insufficent.

In the above case we get line_ip = 1, and (line_ip - start) is positive so our offset < 0 check does not catch it.

Fix this by adding an unsigned comparison against start.

---

index d102716..a791d23 100644
@@ -809,7 +809,7 @@ static int symbol__parse_objdump_line(struct symbol *sym, struct map *map,
 		    end = map__rip_2objdump(map, sym->end);
 
 		offset = line_ip - start;
-		if (offset < 0 || (u64)line_ip > end)
+		if (offset < 0 || (u64)line_ip < start || (u64)line_ip > end)
 			offset = -1;
 		else
 			parsed_line = tmp2 + 1;