lora: sx1276: Add missing RtcTick2Ms function definition

RtcTick2Ms function is required for upcoming LoRaWAN support. Hence,
add definition for it.

Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>

drivers/lora/sx1276.c

diff --git a/drivers/lora/sx1276.c b/drivers/lora/sx1276.c
index 8f3f2f8..26a4795 100644
--- a/drivers/lora/sx1276.c
+++ b/drivers/lora/sx1276.c
@@ -164,6 +164,11 @@
 	return milliseconds;
 }
 
+u32_t RtcTick2Ms(uint32_t tick)
+{
+	return tick;
+}
+
 static void sx1276_dio_work_handle(struct k_work *work)
 {
 	int dio = work - dev_data.dio_work;