mtd: rawnand: Fix comments about the use of bufpoi

Clarify these comments which are not very accurate (even wrong in the
read case).
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200507105241.14299-5-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/nand_base.c

@@ -3279,7 +3279,10 @@ static int nand_do_read_ops(struct nand_chip *chip, loff_t from,
 				break;
 			}
 
-			/* Transfer not aligned data */
+			/*
+			 * Copy back the data in the initial buffer when reading
+			 * partial pages or when a bounce buffer is required.
+			 */
 			if (use_bufpoi) {
 				if (!NAND_HAS_SUBPAGE_READ(chip) && !oob &&
 				    !(mtd->ecc_stats.failed - ecc_failures) &&
@@ -4074,7 +4077,10 @@ static int nand_do_write_ops(struct nand_chip *chip, loff_t to,
 		else
 			use_bufpoi = 0;
 
-		/* Partial page write?, or need to use bounce buffer */
+		/*
+		 * Copy the data from the initial buffer when doing partial page
+		 * writes or when a bounce buffer is required.
+		 */
 		if (use_bufpoi) {
 			pr_debug("%s: using write bounce buffer for buf@%p\n",
 					 __func__, buf);