Fix malloc size error in ahci_init_one.

Typically this causes scsi init to corrupt the
devlist and break the coninfo command.
Fix a compiler size warning.

Signed-off-by: Jason Jin <jason.jin@freescale.com>
Signed-off-by: Ed Swarthout <Ed.Swarthout@freescale.com>
Acked-by: Andy Fleming <afleming@freescale.com>