drm/i915: Fix an error handling path in igt_write_huge()

All error handling paths go to 'out', except this one. Be consistent and
also branch to 'out' here.

Fixes: c10a652e ("drm/i915/selftests: Rework context handling in hugepages selftests")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7a036b88671312ee9adc01c74ef5b3376f690b76.1689619758.git.christophe.jaillet@wanadoo.fr