kbuild: fix make -rR breakage

make failed to supply the filename when using make -rR and using $(*F)
to get target filename without extension.
This bug was not reproduceable in small scale but using:
$(basename $(notdir $@)) fixes it with same functionality.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/Kbuild.include

@@ -12,6 +12,11 @@ space   := $(empty) $(empty)
 # contain a comma
 depfile = $(subst $(comma),_,$(@D)/.$(@F).d)
 
+###
+# basetarget equals the filename of the target with no extension.
+# So 'foo/bar.o' becomes 'bar'
+basetarget = $(basename $(notdir $@))
+
 ###
 # Escape single quote for use in echo statements
 escsq = $(subst $(squote),'\$(squote)',$1)