drm/i915/gvt: rename range variable to stride

Range is a bit odd name for what really is stride. Rename. Switch to u32
while at it.

Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.wang.linux@gmail.com>
Cc: intel-gvt-dev@lists.freedesktop.org
Reviewed-by: Zhi Wang <zhiwang@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/8b8d4acee15da07845ed1779d6856d5c3f50a132.1717773890.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>