staging: fbtft: fbtft-core: Fix last line displayed on fbcon

For the special case when fbtft_mkdirty() is called with with -1 for the y
coordinate, the height is truncated by 1.

This isn't required, and causes the last line to not update.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20191011112441.31003-1-alexandru.ardelean@analog.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/fbtft/fbtft-core.c

@@ -317,7 +317,7 @@ static void fbtft_mkdirty(struct fb_info *info, int y, int height)
 	/* special case, needed ? */
 	if (y == -1) {
 		y = 0;
-		height = info->var.yres - 1;
+		height = info->var.yres;
 	}
 
 	/* Mark display lines/area as dirty */