drm/i915/query: Protect tainted function pointer lookup

drm/i915/query: Protect tainted function pointer lookup

Smatch identifies i915_query_ioctl() as being a potential victim of
Spectre due to its use of a tainted user index into a function pointer
array. Use array_index_nospec() to defang the user index before using it
to lookup the function pointer.

Fixes: a446ae2c6e65 ("drm/i915: add query uAPI")
Signed-off-by: Chris Wilson <[email protected]>
Cc: Lionel Landwerlin <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Reviewed-by: Lionel Landwerlin <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]