MIPS: Remove bogus BUG_ON()

Checking for n<0 && n>9 makes no sense because it can never
be true. Moreover, we can have up to 64 vectored interrupts
so BUG_ON(n>9) was wrong anyway.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5909/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>