Input: focaltech - use explicitly signed char type

The recent change of -funsigned-char causes additions of negative
numbers to become additions of large positive numbers, leading to wrong
calculations of mouse movement. Change these casts to be explicitly
signed, to take into account negative offsets.

Fixes: 3bc753c ("kbuild: treat char as always unsigned")
Signed-off-by: Jason A. Donenfeld <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Cc: [email protected]
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217211
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Torokhov <[email protected]>

Author: zx2c4

drivers/input/mouse/focaltech.c

@@ -202,8 +202,8 @@ static void focaltech_process_rel_packet(struct psmouse *psmouse,
 	state->pressed = packet[0] >> 7;
 	finger1 = ((packet[0] >> 4) & 0x7) - 1;
 	if (finger1 < FOC_MAX_FINGERS) {
-		state->fingers[finger1].x += (char)packet[1];
-		state->fingers[finger1].y += (char)packet[2];
+		state->fingers[finger1].x += (s8)packet[1];
+		state->fingers[finger1].y += (s8)packet[2];
 	} else {
 		psmouse_err(psmouse, "First finger in rel packet invalid: %d\n",
 			    finger1);
@@ -218,8 +218,8 @@ static void focaltech_process_rel_packet(struct psmouse *psmouse,
 	 */
 	finger2 = ((packet[3] >> 4) & 0x7) - 1;
 	if (finger2 < FOC_MAX_FINGERS) {
-		state->fingers[finger2].x += (char)packet[4];
-		state->fingers[finger2].y += (char)packet[5];
+		state->fingers[finger2].x += (s8)packet[4];
+		state->fingers[finger2].y += (s8)packet[5];
 	}
 }