kbuild: clean up subdir-ymn calculation in Makefile.clean

# Figure out what we need to build from the various variables

# ==========================================================================

__subdir-y	:= $(patsubst %/,%,$(filter %/, $(obj-y)))

subdir-y	+= $(__subdir-y)

__subdir-m	:= $(patsubst %/,%,$(filter %/, $(obj-m)))

subdir-m	+= $(__subdir-m)

__subdir-	:= $(patsubst %/,%,$(filter %/, $(obj-)))

subdir-		+= $(__subdir-)

# Subdirectories we need to descend into

subdir-ym	:= $(sort $(subdir-y) $(subdir-m))

subdir-ymn      := $(sort $(subdir-ym) $(subdir-))

subdir-ymn := $(sort $(subdir-y) $(subdir-m) $(subdir-) \

		$(patsubst %/,%, $(filter %/, $(obj-y) $(obj-m) $(obj-))))

# Add subdir path