Fix out-of-bounds access of xdir and ydir in farlook

In commit db68395, most of the instances of xdir and ydir here were
changed to u.dx and u.dy, but not all of them. The remaining ones are
out-of-bounds on xdir and ydir, because i is always set to 12 from an
earlier loop and is no longer involved in handling user input. They
should be u.dx and u.dy like the rest.

src/do_name.c

@@ -787,9 +787,8 @@ getpos(coord *ccp, boolean force, const char *goal)
                 dy = u.dy;
                 while (isok(cx + dx, cy + dy)
                        && glyph == glyph_at(cx + dx, cy + dy)
-                       && isok(cx + dx + xdir[i], cy + dy + ydir[i])
-                       && glyph == glyph_at(cx + dx + xdir[i],
-                                            cy + dy + ydir[i])) {
+                       && isok(cx + dx + u.dx, cy + dy + u.dy)
+                       && glyph == glyph_at(cx + dx + u.dx, cy + dy + u.dy)) {
                     dx += u.dx;
                     dy += u.dy;