The warning notes that we'd want a 'w' register here because the size of
the operand is 32-bit, however, the instruction only takes an 'x'
register and so force that using the 'x' modifier on the instruction.

BUG=

Review URL: https://codereview.chromium.org/1817963003

Cr-Commit-Position: refs/heads/master@{#35008}