patch 8.2.3525: option variable name does not match option name

Problem:    Option variable name does not match option name. (Christ van
            Willigen)
Solution:   Rename the variable.
diff --git a/src/optionstr.c b/src/optionstr.c
index bced92d..7f2b04d 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -271,7 +271,7 @@
 #ifdef FEAT_COMPL_FUNC
     check_string_option(&buf->b_p_cfu);
     check_string_option(&buf->b_p_ofu);
-    check_string_option(&buf->b_p_thsfu);
+    check_string_option(&buf->b_p_tsrfu);
 #endif
 #ifdef FEAT_EVAL
     check_string_option(&buf->b_p_tfu);