HID: cp2112: fix incorrect error propagation in cp2112_xfer()

Both cp2112_read_req() and cp2112_write_req() are returning negative
value in cases of error, but cp2112_xfer() is storing the return
value into unsigned size_t-typed 'count'.

Fix this by making 'count' signed type.

Reported-by: fengguang.wu@intel.com
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-cp2112.c

@@ -428,7 +428,7 @@ static int cp2112_xfer(struct i2c_adapter *adap, u16 addr,
 	struct hid_device *hdev = dev->hdev;
 	u8 buf[64];
 	__be16 word;
-	size_t count;
+	ssize_t count;
 	size_t read_length = 0;
 	unsigned int retries;
 	int ret;