kselftest: vm: fix unused variable warning

Remove unused variable from the MDWE test.

[joey.gouly@arm.com: add commit message]
Link: https://lkml.kernel.org/r/20230308190423.46491-4-joey.gouly@arm.com


Fixes: 4cf1fe34 ("kselftest: vm: add tests for memory-deny-write-execute")
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Alexey Izbyshev <izbyshev@ispras.ru>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: nd <nd@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>