[media] radio-si470x-i2c: fix a warning on ia64

[media] radio-si470x-i2c: fix a warning on ia64

on ia64, those warnings appear:
	drivers/media/radio/si470x/radio-si470x-i2c.c:470:12: warning: 'si470x_i2c_suspend' defined but not used [-Wunused-function]
	drivers/media/radio/si470x/radio-si470x-i2c.c:487:12: warning: 'si470x_i2c_resume' defined but not used [-Wunused-function]
They're caused because the PM logic uses this define:
	#define SET_SYSTEM_SLEEP_PM_OPS()
With is only defined for CONFIG_PM_SLEEP.
So, change the logic there to test for CONFIG_PM_SLEEP, instead of
CONFIG_PM.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>