build: fix call to mkdir

Seen during build:
/bin/bash: line 1: @mkdir: command not found

Remove the extra prefix '@', this line is part of a
single operation actually.

Change-Id: I5fc265ae7c2dda01c61b369803d3c30a42a91f70
Signed-off-by: Jean-Mickael Guerin <jean-mickael.guerin@6wind.com>
diff --git a/vlib-api/Makefile.am b/vlib-api/Makefile.am
index a1fab44..150894e 100644
--- a/vlib-api/Makefile.am
+++ b/vlib-api/Makefile.am
@@ -77,6 +77,6 @@
 
 %.api.h: %.api
 	@echo "  APIGEN  " $@ ; 				\
-	@mkdir -p `dirname $@` ;				\
+	mkdir -p `dirname $@` ;					\
 	$(CC) $(CPPFLAGS) -E -P -C -x c $^			\
 	| vppapigen --input - --output $@ --show-name $@
diff --git a/vpp/Makefile.am b/vpp/Makefile.am
index 15f8d12..06ec713 100644
--- a/vpp/Makefile.am
+++ b/vpp/Makefile.am
@@ -82,7 +82,7 @@
 
 %.api.h: %.api
 	@echo "  APIGEN  " $@ ;					\
-	@mkdir -p `dirname $@` ;				\
+	mkdir -p `dirname $@` ;					\
 	$(CC) $(CPPFLAGS) -E -P -C -x c $^			\
 	| vppapigen --input - --output $@ --show-name $@