selftests/mm: virtual_address_range: Switch to ksft_exit_fail_msg

mmap() must not succeed in validate_lower_address_hint(), for if it does,
it is a bug in mmap() itself.  Reflect this behaviour with
ksft_exit_fail_msg().  While at it, do some formatting changes.

Link: https://lkml.kernel.org/r/20240314122250.68534-1-dev.jain@arm.com


Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>