drm/i915: avoid uninitialised var in eb_parse()

drm/i915: avoid uninitialised var in eb_parse()

The backport of c9d9fdbc108af8915d3f497bbdf3898bf8f321b8 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>