aha1542: split out code from aha1542_hw_init

Split out bus times related block of aha1542_hw_init into separate function
aha1542_set_bus_times.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>