extmod/vfs_fat: getcwd(): Use mp_obj_new_exception_arg1().

Copy-paste issue, with the original mistake in stmhal.

extmod/vfs_fat.c

@@ -145,7 +145,7 @@ STATIC mp_obj_t fat_vfs_getcwd(mp_obj_t vfs_in) {
     FRESULT res = f_getcwd(buf, sizeof buf);
 
     if (res != FR_OK) {
-        nlr_raise(mp_obj_new_exception_msg_varg(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(fresult_to_errno_table[res])));
+        nlr_raise(mp_obj_new_exception_arg1(&mp_type_OSError, MP_OBJ_NEW_SMALL_INT(fresult_to_errno_table[res])));
     }
 
     return mp_obj_new_str(buf, strlen(buf), false);