Fix operator precedence warning in can_api.c

The original code was:
    if(LPC_CAN1->IER | LPC_CAN2->IER != 0) {

This would actually be interpreted as:
    if(LPC_CAN1->IER | (LPC_CAN2->IER != 0)) {
I simplified it to:
    if(LPC_CAN1->IER | LPC_CAN2->IER) {
With the comparison removed, the GCC warning no longer fires since the
user's intent is no longer unclear.  However, the end result should be
the same.

Author: adamgreen

libraries/mbed/targets/hal/TARGET_NXP/TARGET_LPC176X/can_api.c

@@ -164,7 +164,7 @@ void can_irq_set(can_t *obj, CanIrqType type, uint32_t enable) {
     obj->dev->MOD &= ~(1);
 
     // Enable NVIC if at least 1 interrupt is active
-    if(LPC_CAN1->IER | LPC_CAN2->IER != 0) {
+    if(LPC_CAN1->IER | LPC_CAN2->IER) {
         NVIC_SetVector(CAN_IRQn, (uint32_t) &can_irq_n);
         NVIC_EnableIRQ(CAN_IRQn);
     }