selftests/mm: mremap_test: use sscanf to parse /proc/self/maps

selftests/mm: mremap_test: use sscanf to parse /proc/self/maps

Enforce consistency across files by avoiding two separate functions to
parse /proc/self/maps, replacing them with a simple sscanf().

Link: https://lkml.kernel.org/r/20240330173557.2697684-4-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>