Dircache: Fix a tiny-block reclaim bug

Logic left over from before switching from NULL-terminated to
counted strings would prevent a single-byte tiny free block gap
from being properly reclaimed into free string bytes.

Due to rarity, not as disasterous to functionality so much as
wrong.

Change-Id: I68e0875b04bb0ab6cdead0fdf535144b9c1bc13e

firmware/common/dircache.c

@@ -849,7 +849,7 @@ static void free_name(int nameidx, size_t size)
     while (beg[-1] == 0xfe)
         --beg;
 
-    while (end[1] == 0xfe)
+    while (end[0] == 0xfe)
         ++end;
 
     size = end - beg;