[dif, otbn] Fix typo

Signed-off-by: Pirmin Vogel <vogelpi@lowrisc.org>
diff --git a/sw/device/lib/dif/dif_otbn.c b/sw/device/lib/dif/dif_otbn.c
index 0bd6532..b840c37 100644
--- a/sw/device/lib/dif/dif_otbn.c
+++ b/sw/device/lib/dif/dif_otbn.c
@@ -165,7 +165,7 @@
 dif_result_t dif_otbn_dmem_read(const dif_otbn_t *otbn, uint32_t offset_bytes,
                                 void *dest, size_t len_bytes) {
   if (otbn == NULL || dest == NULL ||
-      !check_offset_len(offset_bytes, len_bytes, OTBN_IMEM_SIZE_BYTES)) {
+      !check_offset_len(offset_bytes, len_bytes, OTBN_DMEM_SIZE_BYTES)) {
     return kDifBadArg;
   }