patch 8.0.0448: some macros are in lower case

Problem:    Some macros are in lower case, which can be confusing.
Solution:   Make a few lower case macros upper case.
diff --git a/src/spell.c b/src/spell.c
index f124ef2..1e1f03f 100644
--- a/src/spell.c
+++ b/src/spell.c
@@ -1603,7 +1603,7 @@
      * though...
      */
     lnum = wp->w_cursor.lnum;
-    clearpos(&found_pos);
+    CLEAR_POS(&found_pos);
 
     while (!got_int)
     {
@@ -8545,7 +8545,7 @@
     set_option_value((char_u*)"spl",  dummy, spl, OPT_LOCAL);
     vim_free(spl);
 
-    if (!bufempty())
+    if (!BUFEMPTY())
 	return;
 
     spell_dump_compl(NULL, 0, NULL, eap->forceit ? DUMPFLAG_COUNT : 0);