Input: ads7846 - simplify support of external vREF (and ads7843)

This updates the ads7846 driver to handle external vREF (required
on boards using ads7843 chips) without module parameters, and also
removes a needless variable with its associated bogus gcc warning.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/include/linux/spi/ads7846.h b/include/linux/spi/ads7846.h
index 334d314..daf7440 100644
--- a/include/linux/spi/ads7846.h
+++ b/include/linux/spi/ads7846.h
@@ -14,7 +14,8 @@
 struct ads7846_platform_data {
 	u16	model;			/* 7843, 7845, 7846. */
 	u16	vref_delay_usecs;	/* 0 for external vref; etc */
-	int	keep_vref_on:1;		/* set to keep vref on for differential
+	u16	vref_mv;		/* external vref value, milliVolts */
+	bool	keep_vref_on;		/* set to keep vref on for differential
 					 * measurements as well */
 
 	/* Settling time of the analog signals; a function of Vcc and the