can: uapi: can.h: Fix can error class mask dir path

The CAN error masks header file is in the
include/uapi directory.

Fix the path in the header to the correct location.
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

include/uapi/linux/can.h

@@ -77,7 +77,7 @@ typedef __u32 canid_t;
 /*
  * Controller Area Network Error Message Frame Mask structure
  *
- * bit 0-28	: error class mask (see include/linux/can/error.h)
+ * bit 0-28	: error class mask (see include/uapi/linux/can/error.h)
  * bit 29-31	: set to zero
  */
 typedef __u32 can_err_mask_t;