Use t9 for the call to C functions instead of t8, since t9 must be used
according to MIPS ABI. This saves us one unneccessary move.

TEST=
BUG=

Change-Id: Ic4caf104e043789f0e05930488a48b07c0e134c2
Reviewed-on: https://chromium-review.googlesource.com/844554Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#50309}