drm/i915/selftests: Fix spelling mistake "initialiased" -> "initialised"

There is a spelling mistake in a pr_err error message. Fix it.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231209230541.4055786-1-colin.i.king@gmail.com