MIPS: Use uasm_i_ds{r,l}l_safe() instead of uasm_i_ds{r,l}l() in tlbex.c

This makes the code somewhat cleaner while reducing the risk of shift
amount overflows when various page table related options are changed.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/1154/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>