drm/radeon/kms: fix for hw i2c

use the i2c pads to drive SDA

Possible fix for fdo bug 26430

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon_i2c.c b/drivers/gpu/drm/radeon/radeon_i2c.c
index 4ae50c1..5d93418 100644
--- a/drivers/gpu/drm/radeon/radeon_i2c.c
+++ b/drivers/gpu/drm/radeon/radeon_i2c.c
@@ -291,6 +291,7 @@
 	prescale = radeon_get_i2c_prescale(rdev);
 
 	reg = ((prescale << RADEON_I2C_PRESCALE_SHIFT) |
+	       RADEON_I2C_DRIVE_EN |
 	       RADEON_I2C_START |
 	       RADEON_I2C_STOP |
 	       RADEON_I2C_GO);