selftests/move_mount_set_group remove unneeded conversion to bool

The coccinelle report
./tools/testing/selftests/move_mount_set_group/move_mount_set_group_test.c:225:18-23:
WARNING: conversion to bool not needed here
Relational and logical operators evaluate to bool,
explicit conversion is overly verbose and unneeded.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Yang Guang <yang.guang5@zte.com.cn>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>