mtd: bcm47xxpart: fix parsing first block after aligned TRX

After parsing TRX we should skip to the first block placed behind it.
Our code was working only with TRX with length not aligned to the
blocksize. In other cases (length aligned) it was missing the block
places right after TRX.

This fixes calculation and simplifies the comment.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/bcm47xxpart.c

@@ -229,12 +229,10 @@ static int bcm47xxpart_parse(struct mtd_info *master,
 
 			last_trx_part = curr_part - 1;
 
-			/*
-			 * We have whole TRX scanned, skip to the next part. Use
-			 * roundown (not roundup), as the loop will increase
-			 * offset in next step.
-			 */
-			offset = rounddown(offset + trx->length, blocksize);
+			/* Jump to the end of TRX */
+			offset = roundup(offset + trx->length, blocksize);
+			/* Next loop iteration will increase the offset */
+			offset -= blocksize;
 			continue;
 		}