determine whether there was an error (if so, we unmap the slot space
for this device). Use this functionality to tell the attach function
that we couldn't clear the card's buffer.
Also in aesetup(), eliminate the bogus repetition of the error message
we print when the buffer clear actually fails. Noticed by Hauke Fath.
and allow the attach function to override the default watchdog. Also,
do some minor cosmetic surgery (rename bus space tags/handles and some
KNFing I missed the first time around).
