selftests/mm: simplify byte pattern checking in mremap_test

selftests/mm: simplify byte pattern checking in mremap_test

The original version of mremap_test (7df666253f26: "kselftests: vm: add
mremap tests") validated remapped contents byte-by-byte and printed a
mismatch index in case the bytes streams didn't match.  That was rather
inefficient, especially also if the test passed.

Later, commit 7033c6cc9620 ("selftests/mm: mremap_test: optimize execution
time from minutes to seconds using chunkwise memcmp") used memcmp() on
bigger chunks, to fallback to byte-wise scanning to detect the problematic
index only if it discovered a problem.

However, the implementation is overly complicated (e.g., get_sqrt() is
currently not optimal) and we don't really have to report the exact index:
whoever debugs the failing test can figure that out.

Let's simplify by just comparing both byte streams with memcmp() and not
detecting the exact failed index.

Link: https://lore.kernel.org/20260415044509.579428-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reported-by: Sarthak Sharma <sarthak.sharma@arm.com>
Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>