scripts/genksyms: clean lex/yacc generated files

Add "keywords.hash.c", "lex.lex.c", "parse.tab.c" and "parse.tab.h" to
clean-list so that they get automagically deleted at clean/mrproper
time.

Signed-off-by: Fernando Luis Vazquez Cao<fernando@oss.ntt.co.jp>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/genksyms/Makefile

@@ -11,3 +11,4 @@ HOSTCFLAGS_lex.lex.o := -I$(src)
 # dependencies on generated files need to be listed explicitly
 $(obj)/lex.lex.o: $(obj)/keywords.hash.c $(obj)/parse.tab.h
 
+clean-files	:= keywords.hash.c lex.lex.c parse.tab.c parse.tab.h