drm/i915/switcheroo: check for NULL before dereferencing

drm/i915/switcheroo: check for NULL before dereferencing

Both i915_switcheroo_set_state() and i915_switcheroo_can_switch() check
for i915 == NULL. Commit d2e184f8e16a ("drm/i915/switcheroo: pass
display to HAS_DISPLAY()") started dereferencing it before the NULL
check. Fix it.

Fixes: d2e184f8e16a ("drm/i915/switcheroo: pass display to HAS_DISPLAY()")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202508160035.hmzuKiww-lkp@intel.com/
Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20250818071605.2541523-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>