commit acac4108 upstream.

The "addi" instruction will trap on overflows which is not something
we need in this code, so we replace that with "addiu".

Link: http://www.linux-mips.org/archives/linux-mips/2015-01/msg00430.html
Cc: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>