stm32mp1: fix clean target against check-clean

Remove check-clean target dependency in clean since meaningless
for stm32mp1 platform build environment.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Jerome Forissier <jerome@forissier.org>
diff --git a/stm32mp1.mk b/stm32mp1.mk
index 39789ea..193230e 100644
--- a/stm32mp1.mk
+++ b/stm32mp1.mk
@@ -58,8 +58,7 @@
 	@$(call install_in_binaries,$(ROOT)/out-br/images/sdcard.img)
 	@echo Build for platform $(PLATFORM) completed
 
-clean: tfa-clean optee-os-clean u-boot-clean linux-clean buildroot-clean \
-       check-clean
+clean: tfa-clean optee-os-clean u-boot-clean linux-clean buildroot-clean
 
 include toolchain.mk