Input: drivers/usb/input - fix sparse warnings (signedness)

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/drivers/usb/input/acecad.c b/drivers/usb/input/acecad.c
index be8e924..dd231045 100644
--- a/drivers/usb/input/acecad.c
+++ b/drivers/usb/input/acecad.c
@@ -54,7 +54,7 @@
 	struct input_dev *input;
 	struct urb *irq;
 
-	signed char *data;
+	unsigned char *data;
 	dma_addr_t data_dma;
 };