ide: sgiioc4: Staticize ioc4_ide_attach_one()

ioc4_ide_attach_one() is used only in this file.
Fix the following sparse warnings:

drivers/ide/sgiioc4.c:603:5: warning: symbol 'ioc4_ide_attach_one' was not declared. Should it be static?

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>