drm/i915: Tidy the tail of i915_tiling_ok()

drm/i915: Tidy the tail of i915_tiling_ok()

The current tail breaks the pattern of if (check) return false, which
can catch the reader out. If we move the gen2/3 power-of-two test into
the earlier gen2/3 branch, we can eliminate the contrary tail.

Suggested-by: Tvrtko Ursulin <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
Cc: Tvrtko Ursulin <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Tvrtko Ursulin <[email protected]>