video/logo: remove unneeded *.o pattern from clean-files

The pattern *.o is cleaned up globally by the top Makefile.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

drivers/video/logo/Makefile

@@ -56,4 +56,4 @@ $(obj)/%_gray256.c: $(src)/%_gray256.pgm $(pnmtologo) FORCE
 	$(call if_changed,logo)
 
 # Files generated that shall be removed upon make clean
-clean-files := *.o *_mono.c *_vga16.c *_clut224.c *_gray256.c
+clean-files := *_mono.c *_vga16.c *_clut224.c *_gray256.c