patch 8.1.0685: get_buf_tv() is named inconsistently

Problem:    get_buf_tv() is named inconsistently.
Solution:   Rename it to tv_get_buf(). (Yegappan Lakshmanan, closes #3759)
diff --git a/src/textprop.c b/src/textprop.c
index 578f6e9..53b43e1 100644
--- a/src/textprop.c
+++ b/src/textprop.c
@@ -130,7 +130,7 @@
     di = dict_find(arg->vval.v_dict, (char_u *)"bufnr", -1);
     if (di != NULL)
     {
-	*buf = get_buf_tv(&di->di_tv, FALSE);
+	*buf = tv_get_buf(&di->di_tv, FALSE);
 	if (*buf == NULL)
 	    return FAIL;
     }
@@ -533,7 +533,7 @@
     di = dict_find(dict, (char_u *)"bufnr", -1);
     if (di != NULL)
     {
-	buf = get_buf_tv(&di->di_tv, FALSE);
+	buf = tv_get_buf(&di->di_tv, FALSE);
 	if (buf == NULL)
 	    return;
     }