In commit 652562e5ff06 ("can: length: can_fd_len2dlc(): simplify length
calculcation") the readability of the code degraded and became more error
prone. To counteract this, partially convert that patch and replace open coded
values (of the original code) with proper defines.
Also double check the correct length mapping table size at build time.

Cc: Vincent MAILHOL <redacted>
Fixes: 652562e5ff06 ("can: length: can_fd_len2dlc(): simplify length calculcation")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
 drivers/net/can/dev/length.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/dev/length.c b/drivers/net/can/dev/length.c
index d35c4e82314d..d085cb26d00d 100644
--- a/drivers/net/can/dev/length.c
+++ b/drivers/net/can/dev/length.c

@@ -25,16 +25,21 @@ static const u8 len2dlc[] = {
 	11, 11, 11, 11,			/* 17 - 20 */
 	12, 12, 12, 12,			/* 21 - 24 */
 	13, 13, 13, 13, 13, 13, 13, 13,	/* 25 - 32 */
 	14, 14, 14, 14, 14, 14, 14, 14,	/* 33 - 40 */
 	14, 14, 14, 14, 14, 14, 14, 14,	/* 41 - 48 */
+	15, 15, 15, 15, 15, 15, 15, 15,	/* 49 - 56 */
+	15, 15, 15, 15, 15, 15, 15, 15	/* 57 - 64 */
 };
 
 /* map the sanitized data length to an appropriate data length code */
 u8 can_fd_len2dlc(u8 len)
 {
-	if (len >= ARRAY_SIZE(len2dlc))
+	/* check for length mapping table size at build time */
+	BUILD_BUG_ON(ARRAY_SIZE(len2dlc) < CANFD_MAX_DLEN + 1);