Makefile: remove unused rule from Makefile

Signed-off-by: Federico Vaga <federico.vaga@gmail.com>

buffers/Makefile

@@ -4,6 +4,3 @@ EXTRA_CFLAGS += -I$(obj)/../include/
 
 # zio-buf-kmalloc.o is now part of zio-core
 obj-m = zio-buf-vmalloc.o
-
-all:
-	$(MAKE) -C $(LINUX) M=$(shell /bin/pwd) modules

drivers/Makefile

@@ -7,6 +7,3 @@ obj-m += zio-gpio.o
 ifdef CONFIG_SPI
 obj-m += zio-ad788x.o
 endif
-
-all:
-	$(MAKE) -C $(LINUX) M=$(shell /bin/pwd) modules

triggers/Makefile

@@ -5,6 +5,3 @@ EXTRA_CFLAGS += -I$(obj)/../include/
 # zio-trig-user.o is now part of zio-core
 obj-m = zio-trig-timer.o
 obj-m += zio-trig-irq.o
-
-all:
-	$(MAKE) -C $(LINUX) M=$(shell /bin/pwd) modules