roi_harness: Add .frm files to make clean target

Signed-off-by: Tomasz Michalak <tmichalak@antmicro.com>

minitests/roi_harness/Makefile.mini

diff --git a/minitests/roi_harness/Makefile.mini b/minitests/roi_harness/Makefile.mini
index 4fff99d..ae650a8 100644
--- a/minitests/roi_harness/Makefile.mini
+++ b/minitests/roi_harness/Makefile.mini
@@ -10,6 +10,7 @@
 	@rm -f *.bits
 	@rm -f *.fasm
 	@rm -f *.log
+	@rm -f *.frm
 	@rm -rf build
 
 .PHONY: all clean