fvp, ts: fix clean targets

Before cmake configuration is done, or after runnig ts specific
realclean targets the out/ts-build directory is not present. This
makes ts clean targets fail, which block the clean target chain.
Modify the ts clean targets to ignore errors and let the clean chain
fully execute.

Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Gyorgy Szing <gyorgy.szing@arm.com>

trusted-services.mk

@@ -67,7 +67,7 @@ ffa-$1-sp:
 
 .PHONY: ffa-$1-sp-clean
 ffa-$1-sp-clean:
-	$$(MAKE) -C $(TS_BUILD_PATH)/$1 clean
+	- $$(MAKE) -C $(TS_BUILD_PATH)/$1 clean
 
 .PHONY: ffa-$1-sp-realclean
 ffa-$1-sp-realclean:
@@ -179,7 +179,7 @@ endif
 
 .PHONY: ffa-$1-clean
 ffa-$1-clean:
-	$$(MAKE) -C $(TS_BUILD_PATH)/$1 clean
+	- $$(MAKE) -C $(TS_BUILD_PATH)/$1 clean
 
 .PHONY: ffa-$1-realclean
 ffa-$1-realclean: