selftests/mm: fix "warning: expression which evaluates to zero..." in mlock2-tests.c

The stop variable is a char*, and the code was assigning a char value to
it. This was generating a warning when compiling with clang.

However, as both David and Peter pointed out, stop is not even used
after the problematic assignment to a char type. So just delete that
line entirely.

Link: https://lkml.kernel.org/r/20230606071637.267103-4-jhubbard@nvidia.comSigned-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/mlock2-tests.c

@@ -50,7 +50,6 @@ static int get_vm_area(unsigned long addr, struct vm_boundaries *area)
 			printf("cannot parse /proc/self/maps\n");
 			goto out;
 		}
-		stop = '\0';
 
 		sscanf(line, "%lx", &start);
 		sscanf(end_addr, "%lx", &end);