switch ->is_visible() to returning umode_t

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Conflicts:
	drivers/hwmon/max1668.c
	drivers/infiniband/ulp/iser/iscsi_iser.c
	drivers/platform/x86/asus-wmi.c
	drivers/platform/x86/ideapad-laptop.c
	drivers/scsi/be2iscsi/be_iscsi.c
	drivers/scsi/be2iscsi/be_iscsi.h
	drivers/scsi/bnx2i/bnx2i_iscsi.c
	drivers/scsi/cxgbi/libcxgbi.c
	drivers/scsi/cxgbi/libcxgbi.h
	drivers/scsi/iscsi_boot_sysfs.c
	drivers/scsi/iscsi_tcp.c
	drivers/scsi/qla4xxx/ql4_os.c
	drivers/scsi/scsi_transport_iscsi.c
	drivers/staging/iio/adc/ad7192.c
	include/linux/iscsi_boot_sysfs.h
	include/scsi/scsi_transport_iscsi.h