build: Fix parallel build

Fix parallel build where parser.h won't have been generated when
we're trying to compile kword itself.

 YACC   tools/parser.c
 LEX    tools/lexer.c
conflicts: 3 shift/reduce
 CC     tools/kword.o
tools/kword.c:36:20: fatal error: parser.h: No such file or directory
compilation terminated.
diff --git a/Makefile.tools b/Makefile.tools
index 405a42b..797b53d 100644
--- a/Makefile.tools
+++ b/Makefile.tools
@@ -12,6 +12,8 @@
 noinst_PROGRAMS += tools/avinfo tools/ppporc \
 				tools/hcieventmask tools/hcisecfilter
 
+tools/kword.c: tools/parser.h
+
 tools_rfcomm_SOURCES = tools/main.c tools/parser.y tools/lexer.l \
 					tools/kword.h tools/kword.c
 EXTRA_tools_rfcomm_SOURCES = tools/parser.h tools/parser.c \