tests/driver_mpl3115a2: simplified Makefile

tests/driver_mpl3115a2/Makefile

@@ -6,15 +6,12 @@ FEATURES_REQUIRED = periph_i2c
 USEMODULE += mpl3115a2
 USEMODULE += xtimer
 
-ifneq (,$(TEST_MPL3115A2_I2C))
-  CFLAGS += -DTEST_MPL3115A2_I2C=$(TEST_MPL3115A2_I2C)
-else
-  CFLAGS += -DTEST_MPL3115A2_I2C=I2C_0
-endif
-ifneq (,$(TEST_MPL3115A2_ADDR))
-  CFLAGS += -DTEST_MPL3115A2_ADDR=$(TEST_MPL3115A2_ADDR)
-else
-  CFLAGS += -DTEST_MPL3115A2_ADDR=0x60
-endif
+# set default device parameters in case they are undefined
+TEST_MPL3115A2_I2C  ?= I2C_0
+TEST_MPL3115A2_ADDR ?= 0x60
+
+# export parameters
+CFLAGS += -DTEST_MPL3115A2_I2C=$(TEST_MPL3115A2_I2C)
+CFLAGS += -DTEST_MPL3115A2_ADDR=$(TEST_MPL3115A2_ADDR)
 
 include $(RIOTBASE)/Makefile.include