include/vki/vki-scnums-arm64-linux.h use correct __NR_lseek define.

This caused memcheck/tests/linux/proc-auxv.vgtest to fail because
our internal VG(lseek) would return ENOSYS.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14383 a5019735-40e9-0310-863c-91ae7b9d1cf9