[media] imon: fix Knob event interpretation issues on ARM

Events for the iMon Knob pad where not correctly interpreted on ARM,
resulting in buggy mouse movements (cursor going straight out of the
screen), key pad only generating KEY_RIGHT and KEY_DOWN events.
A reproducer is:
int main(int argc, char ** argv)
{
        char rel_x = 0x00; printf("rel_x:%d @%s:%d\n", rel_x, __FILE__, __LINE__);
        rel_x = 0x0f; printf("rel_x:%d @%s:%d\n", rel_x, __FILE__, __LINE__);
        rel_x |= ~0x0f; printf("rel_x:%d @%s:%d\n", rel_x, __FILE__, __LINE__);
        return 0;
}
(running on x86 or amd64)
$ ./test
rel_x:0 @test.c:6
rel_x:15 @test.c:7
rel_x:-1 @test.c:8
(running on armv6)
rel_x:0 @test.c:6
rel_x:15 @test.c:7
rel_x:255 @test.c:8
Forcing the rel_x and rel_y variables as signed char fixes the issue.

Reference: http://www.arm.linux.org.uk/docs/faqs/signedchar.php

Signed-off-by: Alexandre Lissy <alexandrelissy@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/rc/imon.c

@@ -1221,7 +1221,7 @@ static u32 imon_panel_key_lookup(u64 code)
 static bool imon_mouse_event(struct imon_context *ictx,
 			     unsigned char *buf, int len)
 {
-	char rel_x = 0x00, rel_y = 0x00;
+	signed char rel_x = 0x00, rel_y = 0x00;
 	u8 right_shift = 1;
 	bool mouse_input = true;
 	int dir = 0;
@@ -1297,7 +1297,7 @@ static void imon_touch_event(struct imon_context *ictx, unsigned char *buf)
 static void imon_pad_to_keys(struct imon_context *ictx, unsigned char *buf)
 {
 	int dir = 0;
-	char rel_x = 0x00, rel_y = 0x00;
+	signed char rel_x = 0x00, rel_y = 0x00;
 	u16 timeout, threshold;
 	u32 scancode = KEY_RESERVED;
 	unsigned long flags;