aha1542: Allocate memory before taking a lock

The driver currently calls kmalloc with GFP_KERNEL while holding a lock.
Fix it by doing the allocation earlier, before taking the lock.

Tested on AHA-1542B.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: James Bottomley <JBottomley@Odin.com>