assemble: reduce the priority of "mask not permitted" error

Per BR 75, the "mask not permitted" error is a little too persistent.

Fixes: https://github.com/netwide-assembler/nasm/pull/75 (hopefully)
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

asm/assemble.c

diff --git a/asm/assemble.c b/asm/assemble.c
index 3c1b65c..4aeb2d4 100644
--- a/asm/assemble.c
+++ b/asm/assemble.c
@@ -30,9 +30,9 @@
     MERR_OPSIZEINVAL,
     MERR_OPSIZEMISSING,
     MERR_OPSIZEMISMATCH,
+    MERR_MASKNOTHERE,
     MERR_BRNOTHERE,
     MERR_BRNUMMISMATCH,
-    MERR_MASKNOTHERE,
     MERR_DECONOTHERE,
     MERR_BADZU,
     MERR_MEMZU,