Remove recursive unmount

Sigh, Kokoro's umount doesn't support recursive:
sudo umount -R
/tmpfs/src/git/out/target/product/imx8m_phanbell/obj/ROOTFS/rootfs
umount: invalid option -- 'R'
Usage: umount -h | -V
       umount -a [-d] [-f] [-r] [-n] [-v] [-t vfstypes] [-O opts]
       umount [-d] [-f] [-r] [-n] [-v] special | node...
make: *** [/tmpfs/src/git/out/target/product/imx8m_phanbell/obj/ROOTFS/rootfs.raw.img] Error 1

- Remove the -R option from umount commands. Also add an unmount for
/dev/pts, as it was being unmounted by way of the recursive unmount.

Change-Id: I4e2bc0eb463db1a31d9bf9ffcd525c0f24958406
diff --git a/rootfs.mk b/rootfs.mk
index 6b7cd9f..94e25d1 100644
--- a/rootfs.mk
+++ b/rootfs.mk
@@ -64,7 +64,8 @@
 	echo "enterprise	ALL=(ALL) ALL" |sudo tee -a $(ROOTFS_DIR)/etc/sudoers
 
 	sudo $(ROOTDIR)/build/fix_permissions.sh -p $(ROOTDIR)/build/permissions.txt -t $(ROOTFS_DIR)
-	sudo umount -R $(ROOTFS_DIR)/{dev,proc,sys}
+	sudo umount $(ROOTFS_DIR)/dev/pts
+	sudo umount $(ROOTFS_DIR)/{dev,proc,sys}
 
 $(ROOTFS_RAW_IMG): $(DEBOOTSTRAP_TARBALL) $(ROOTDIR)/build/debootstrap.mk $(ROOTDIR)/build/preamble.mk
 	+make -f $(ROOTDIR)/build/debootstrap.mk validate-bootstrap-tarball
@@ -79,7 +80,7 @@
 		$(DEBOOTSTRAP_ARGS) \
 		--unpack-tarball=$(DEBOOTSTRAP_TARBALL) \
 		stretch $(ROOTFS_DIR)
-	sudo umount -R $(ROOTFS_DIR)
+	sudo umount $(ROOTFS_DIR)
 	sudo rmdir $(ROOTFS_DIR)
 	sudo sync $(ROOTFS_RAW_IMG)
 	sudo chown ${USER} $(ROOTFS_RAW_IMG)
@@ -95,7 +96,7 @@
 	+make -f $(ROOTDIR)/build/kernel.mk modules_install
 	+make -f $(ROOTDIR)/build/rootfs.mk adjustments
 
-	sudo umount -R $(ROOTFS_DIR)
+	sudo umount $(ROOTFS_DIR)
 	sudo rmdir $(ROOTFS_DIR)
 	sudo sync $(ROOTFS_PATCHED_IMG)
 	sudo chown ${USER} $(ROOTFS_PATCHED_IMG)