tests/driver_pcd8544: simplified Makefile

tests/driver_pcd8544/Makefile

@@ -6,17 +6,16 @@ FEATURES_REQUIRED = periph_gpio periph_spi
 USEMODULE += shell
 USEMODULE += pcd8544
 
-ifeq (,$(TEST_PCD8544_SPI))
-  CFLAGS += -DTEST_PCD8544_SPI=SPI_0
-endif
-ifeq (,$(TEST_PCD8544_CS))
-  CFLAGS += -DTEST_PCD8544_CS=GPIO_PIN\(0,0\)
-endif
-ifeq (,$(TEST_PCD8544_RESET))
-  CFLAGS += -DTEST_PCD8544_RESET=GPIO_PIN\(0,1\)
-endif
-ifeq (,$(TEST_PCD8544_MODE))
-  CFLAGS += -DTEST_PCD8544_MODE=GPIO_PIN\(0,2\)
-endif
+# set default device parameters in case they are undefined
+TEST_PCD8544_SPI   ?= SPI_0
+TEST_PCD8544_CS    ?= GPIO_PIN\(0,0\)
+TEST_PCD8544_RESET ?= GPIO_PIN\(0,1\)
+TEST_PCD8544_MODE  ?= GPIO_PIN\(0,2\)
+
+# export parameters
+CFLAGS += -DTEST_PCD8544_SPI=$(TEST_PCD8544_SPI)
+CFLAGS += -DTEST_PCD8544_CS=$(TEST_PCD8544_CS)
+CFLAGS += -DTEST_PCD8544_RESET=$(TEST_PCD8544_RESET)
+CFLAGS += -DTEST_PCD8544_MODE=$(TEST_PCD8544_MODE)
 
 include $(RIOTBASE)/Makefile.include