While here, check for errors from bus_generic_detach and move it to
the start of detach if necessary.
Differential Revision: https://reviews.freebsd.org/D47969
Some devices like Apple HID-over-SPI may contain more than one report
descriptors necessitating creation of multiple hidbus children.
Add indentificator of child devices to distinct them.
No functional changes intended.
Differential Revision: https://reviews.freebsd.org/D41246