selftests/mount: remove unneeded conversion to bool

The coccinelle report
./tools/testing/selftests/mount/unprivileged-remount-test.c:285:54-59:
WARNING: conversion to bool not needed here
./tools/testing/selftests/mount/unprivileged-remount-test.c:207:54-59:
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>