HID: sony: Fix unused function warning

Compiling this driver without setting "CONFIG_SONY_FF" generates the
following warning:

	drivers/hid/hid-sony.c:2358:20: warning: unused function
	'sony_send_output_report' [-Wunused-function]
	static inline void sony_send_output_report(struct sony_sc *sc)
	                   ^
	1 warning generated.

Add the missing preprocessor check to fix it.

Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>