vdso: suppress not ELF vDSO error

When mapping compatible vDSO in restorer blob (with vdso_map_compat),
we don't know if the kernel will map firstly vvar pages or vdso pages.
So we attempt search by checking ELF header magic on those pages.
Which leads to following "errors", which this patch hides:
pie: 1: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 1: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 7: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 7: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 6: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 6: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 4: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 5: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 4: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
pie: 5: Error (pie/util-vdso-elf32.c:87): vdso: Elf header magic misma>
(for two vvar pages and 5 processes being restored).

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>