intelspi: don't leak spibus children on detach

[yuripv]

Test Plan

1. kldload intelspi
2. kldunload intelspi

[kib]

sys/dev/intel/spi.c

500

There is device delete_children(9). It would be much more convenient to use there.

But I suspect that intelspi should be considered bus and then bus_generic_detach(9) used instead. See the call for bus generic_attach() above.

[yuripv]

use bus_generic_detach().

[yuripv]

sys/dev/intel/spi.c

500

Even better, works the same.