MIPS: fw: sni: Fix out of bounds init of o32 stack

[ Upstream commit efcb529694c3b707dc0471b312944337ba16e4dd ]

Use ARRAY_SIZE to caluculate the top of the o32 stack.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>