hw/pl190.c: Fix writing of default vector address

hw/pl190.c: Fix writing of default vector address

The PL190 implementation keeps the default vector address
in vect_addr[16], but we weren't using this for writes to
the DEFVECTADDR register. As a result of this fix the
default_addr structure member is unused and we can delete it.

Reported-by: Himanshu Chauhan <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Signed-off-by: Aurelien Jarno <[email protected]>