drm/xe: Make xe_modparam.force_vram_bar_size signed

drm/xe: Make xe_modparam.force_vram_bar_size signed

vram_bar_size is registered as an int module parameter and is documented
to accept negative values to disable BAR resizing.
Store it as an int in xe_modparam as well, so negative values work as
intended and the module_param type matches.

Fixes: 80742a1aa26e ("drm/xe: Allow to drop vram resizing")
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Link: https://patch.msgid.link/20260202181853.1095736-2-shuicheng.lin@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>