Fix clang warnings

Explicitly convert unsigned int to uint64_t before converting them to
uint16x4_t or uint8x8_t.

BUG=chromium:1035559

Change-Id: I7d0084c1ab9393063a15972a714d89db4e5e1afe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/260981
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed