patch 8.0.0451: some macros are in lower case

Problem:    Some macros are in lower case.
Solution:   Make a few more macros upper case. Avoid lower case macros use an
            argument twice.
diff --git a/src/syntax.c b/src/syntax.c
index b13bd93..12de244 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -3211,12 +3211,12 @@
 	if (off > 0)
 	{
 	    while (off-- > 0 && *p != NUL)
-		mb_ptr_adv(p);
+		MB_PTR_ADV(p);
 	}
 	else if (off < 0)
 	{
 	    while (off++ < 0 && base < p)
-		mb_ptr_back(base, p);
+		MB_PTR_BACK(base, p);
 	}
 	col = (int)(p - base);
     }
@@ -3265,12 +3265,12 @@
 	if (off > 0)
 	{
 	    while (off-- && *p != NUL)
-		mb_ptr_adv(p);
+		MB_PTR_ADV(p);
 	}
 	else if (off < 0)
 	{
 	    while (off++ && base < p)
-		mb_ptr_back(base, p);
+		MB_PTR_BACK(base, p);
 	}
 	col = (int)(p - base);
     }