x86/platform/ts5500: Use the DEVICE_ATTR_RO() macro

Use the DEVICE_ATTR_RO() helper macro to simplify the declaration
of read-only sysfs attributes in the TS5500 code..

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Savoir-faire Linux Inc. <kernel@savoirfairelinux.com>
Link: http://lkml.kernel.org/r/1404860269-11837-2-git-send-email-vivien.didelot@savoirfairelinux.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>