tests/driver_dht: simplified Makefile

tests/driver_dht/Makefile

@@ -3,26 +3,20 @@ include ../Makefile.tests_common
 
 FEATURES_REQUIRED = periph_gpio
 
-# define default pin mappings for some boards:
-ifneq (,$(filter stm32f4discovery,$(BOARD)))
-  export DHT_GPIO ?= GPIO_PIN\(4,3\)
-endif
-
 USEMODULE += dht
 USEMODULE += xtimer
 
-ifneq (,$(DHT_TYPE))
-  CFLAGS += -DDHT_TYPE=$(DHT_TYPE)
-else
-  # set random default
-  CFLAGS += -DDHT_TYPE=DHT11
+# define parameters for selected boards
+ifneq (,$(filter stm32f4discovery,$(BOARD)))
+  DHT_GPIO ?= GPIO_PIN\(4,3\)
 endif
 
-ifneq (,$(DHT_GPIO))
-  CFLAGS += -DDHT_GPIO=$(DHT_GPIO)
-else
-  # set random default
-  CFLAGS += -DDHT_GPIO=GPIO_PIN\(0,0\)
-endif
+# set default device parameters in case they are undefined
+DHT_GPIO ?= GPIO_PIN\(0,0\)
+DHT_TYPE ?= DHT11
+
+# export parameters
+CFLAGS += -DDHT_TYPE=$(DHT_TYPE)
+CFLAGS += -DDHT_GPIO=$(DHT_GPIO)
 
 include $(RIOTBASE)/Makefile.include