[MTD] [INFTL] Fix infinite loop in INFTL_foldchain

When iterating over a chain in reverse (oldest block first), this
patch correctly marks the PUtable[] entry of the second to last erase
block of a chain as BLOCK_NIL, regardless of whether or not it can
format the last block successfully. Before, the second to last block
was only marked as pointing to BLOCK_NIL if INFTL_formatblock()
succeeded on the last block of the chain, which could potentially
result in an infinite loop if the block was worn out and refused to
format.
Signed-off-by: Daniel Rosenthal <danielrosenthal@acm.org>
Acked-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/inftlcore.c

@@ -388,6 +388,10 @@ static u16 INFTL_foldchain(struct INFTLrecord *inftl, unsigned thisVUC, unsigned
 		if (thisEUN == targetEUN)
 			break;
 
+		/* Unlink the last block from the chain. */
+		inftl->PUtable[prevEUN] = BLOCK_NIL;
+
+		/* Now try to erase it. */
 		if (INFTL_formatblock(inftl, thisEUN) < 0) {
 			/*
 			 * Could not erase : mark block as reserved.
@@ -396,7 +400,6 @@ static u16 INFTL_foldchain(struct INFTLrecord *inftl, unsigned thisVUC, unsigned
 		} else {
 			/* Correctly erased : mark it as free */
 			inftl->PUtable[thisEUN] = BLOCK_FREE;
-			inftl->PUtable[prevEUN] = BLOCK_NIL;
 			inftl->numfreeEUNs++;
 		}
 	}