Staging: ipack: fix build failure in powerpc allyesconfig

Caused by commit 187e4782 ("Staging: ipack: Read the ID space during
device registration").

drivers/staging/ipack/ipack.c: In function 'ipack_device_read_id':
drivers/staging/ipack/ipack.c:291:2: error: implicit declaration of function
	'ioread8' [-Werror=implicit-function-declaration]
drivers/staging/ipack/ipack.c:309:3: error: implicit declaration of function
	'ioread16be' [-Werror=implicit-function-declaration]

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>