MIPS: unaligned: Surround load/store macros in do {} while statements

It's best to surround such complex macros with do {} while statements
so they can appear as independent logical blocks when used within other
control blocks.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: <stable@vger.kernel.org> # v3.15+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9502/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>