[PATCH -next] drm/i915: Add missing include file <linux/math64.h>

[Chris Wilson]

Quoting YueHaibing (2020-01-07 13:50:14)
> Fix build error:
> ./drivers/gpu/drm/i915/selftests/i915_random.h: In function i915_prandom_u32_max_state:
> ./drivers/gpu/drm/i915/selftests/i915_random.h:48:23: error:
>  implicit declaration of function mul_u32_u32; did you mean mul_u64_u32_div? [-Werror=implicit-function-declaration]
>   return upper_32_bits(mul_u32_u32(prandom_u32_state(state), ep_ro));
> 
> Reported-by: Hulk Robot <hulkci at huawei.com>
> Fixes: 7ce5b6850b47 ("drm/i915/selftests: Use mul_u32_u32() for 32b x 32b -> 64b result")
> Signed-off-by: YueHaibing <yuehaibing at huawei.com>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris