patch 8.1.2205: sign entry structure has confusing name

Problem:    Sign entry structure has confusing name.
Solution:   Rename signlist_T to sign_entry_T and prefix se_ to the fields.
diff --git a/src/globals.h b/src/globals.h
index 3f883d1..d2c1e33 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -676,7 +676,7 @@
 
 // Iterate through all the signs placed in a buffer
 #define FOR_ALL_SIGNS_IN_BUF(buf, sign) \
-	for (sign = buf->b_signlist; sign != NULL; sign = sign->next)
+	for (sign = buf->b_signlist; sign != NULL; sign = sign->se_next)
 
 // Flag that is set when switching off 'swapfile'.  It means that all blocks
 // are to be loaded into memory.  Shouldn't be global...