->busproc method is used by HDIO_SET_BUSSTATE ioctl but it has no chance
of working as intended (in 2.4.x days) because to issue an ioctl there
is a device node needed and:

- for BUSSTATE_TRISTATE+OFF it is too late (devices are already gone)

- for BUSSTATE_TRISTATE+ON it is too early (devices are not registered yet)

Just remove ->busproc method for now (it was only implemented by hpt366,
siimage and tc86c001 host drivers).

Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>