drm/i915/selftests: fix a couple IS_ERR() vs NULL tests

stable inclusion
from stable-v5.10.132
commit 636e5dbaf097aaf66b6234f0b10598d44ccc8a87
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5YS3T

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=636e5dbaf097aaf66b6234f0b10598d44ccc8a87



--------------------------------

[ Upstream commit 896dcabd ]

The shmem_pin_map() function doesn't return error pointers, it returns
NULL.

Fixes: be1cb55a ("drm/i915/gt: Keep a no-frills swappable copy of the default context state")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220708094104.GL2316@kadam


(cherry picked from commit d50f5a10)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Acked-by: Xie XiuQi <xiexiuqi@huawei.com>