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/os_unix.c b/src/os_unix.c
index 9dd5c34..69868ac 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -6522,7 +6522,7 @@
     int
 mch_has_exp_wildcard(char_u *p)
 {
-    for ( ; *p; mb_ptr_adv(p))
+    for ( ; *p; MB_PTR_ADV(p))
     {
 	if (*p == '\\' && p[1] != NUL)
 	    ++p;
@@ -6546,7 +6546,7 @@
     int
 mch_has_wildcard(char_u *p)
 {
-    for ( ; *p; mb_ptr_adv(p))
+    for ( ; *p; MB_PTR_ADV(p))
     {
 	if (*p == '\\' && p[1] != NUL)
 	    ++p;