drm/i915: avoid uninitialised var in eb_parse()

stable inclusion
from stable-5.10.58
commit 11891adab23daa7e08a8e0c25bebfba9c5b5a579
bugzilla: 176984 https://gitee.com/openeuler/kernel/issues/I4E2P4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=11891adab23daa7e08a8e0c25bebfba9c5b5a579



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

The backport of c9d9fdbc to 5.10 in
6976f3cf34a1a8b791c048bbaa411ebfe48666b1 removed more than it should
have leading to 'batch' being used uninitialised.  The 5.13 backport and
the mainline commit did not remove the portion this patch adds back.

Signed-off-by: Jonathan Gray <jsg@jsg.id.au>
Fixes: 6976f3cf34a1 ("drm/i915: Revert "drm/i915/gem: Asynchronous cmdparser"")
Cc: <stable@vger.kernel.org> # 5.10
Cc: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>