mfd: motorola-cpcap: Disable interrupt for suspend

Otherwise we get spammed with errors on resume after rtcwake:

 cpcap-core spi0.0: Failed to read IRQ status: -108

Note that rtcwake is still capable of waking up the system with
this patch.

Cc: Merlijn Wajer <merlijn@wizzup.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>