bsp/csb336: mc9328mxl correct AITC access in bsp_interrupt_dispatch.

The original version is missing void and result is that (*x >> 16) is
optimized to ldh rX,[rY]. But it is not allowed/supported to access
bus/address range used by AITC by other than 32 bit wide accesses
and 16-bit access results in the data abort exception.
The corrected version works on real hardware and is even
more readable.

Signed-off-by: Pavel Pisa <ppisa@pikron.com>