Input: tsc2007 - make sure that X plate resistance is specified

Abort driver initialization if X plate resistance was not specified in
platform data as it will cause pressure to be always calculated as 0,
and making userspace ignore touch coordinates.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/include/linux/i2c/tsc2007.h b/include/linux/i2c/tsc2007.h
index 591427a..506a9f7 100644
--- a/include/linux/i2c/tsc2007.h
+++ b/include/linux/i2c/tsc2007.h
@@ -5,7 +5,7 @@
 
 struct tsc2007_platform_data {
 	u16	model;				/* 2007. */
-	u16	x_plate_ohms;
+	u16	x_plate_ohms;	/* must be non-zero value */
 	u16	max_rt; /* max. resistance above which samples are ignored */
 	unsigned long poll_delay; /* delay (in ms) after pen-down event
 				     before polling starts */