m68k: amiflop - Get rid of sleep_on calls

Apart from sleep_on() calls that could be easily converted to
wait_event() and completion calls amiflop also used a flag in ms_delay()
and ms_isr() as a custom mutex for ms_delay() without a need for
explicit unlocking.  I converted that to a standard mutex.

The replacement for the unconditional sleep_on() in fd_motor_on() is a
complete_all() together with a INIT_COMPLETION() before the mod_timer()
call.  It appears to me that fd_motor_on() might be called concurrently
and fd_select() does not guarantee mutual exclusivity in the case the
same drive gets selected again.

Signed-off-by: Andreas Bombe <aeb@debian.org>
Acked-by: Jörg Dorchain <joerg@dorchain.net>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>