macintosh/adb-iop: Access current_req and adb_iop_state when inside lock

Drop the redundant local_irq_save/restore() from adb_iop_start() because
the caller has to do it anyway. This is the pattern used in via-macii.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/bbe32b087c7e04d68e2425f6a2df4a414d167c32.1590880623.git.fthain@telegraphics.com.au