Fix mounting /sdcard under recovery.

The CL in [1] changed to create a symlink to /storage/self/primary for
/sdcard. It breaks the mount of /sdcard under recovery.

[1] commit 595003a3d06a13862052ef2f4f578371dae5ad65

Bug: 26509280
Change-Id: I98d02d54d707c2c8826c5ee119cf1a3ffa0c4bc9
diff --git a/core/Makefile b/core/Makefile
index aee792a..3c1c84e 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -920,9 +920,9 @@
 define build-recoveryimage-target
   @echo ----- Making recovery image ------
   $(hide) mkdir -p $(TARGET_RECOVERY_OUT)
-  $(hide) mkdir -p $(TARGET_RECOVERY_ROOT_OUT)/etc $(TARGET_RECOVERY_ROOT_OUT)/tmp
+  $(hide) mkdir -p $(TARGET_RECOVERY_ROOT_OUT)/etc $(TARGET_RECOVERY_ROOT_OUT)/sdcard $(TARGET_RECOVERY_ROOT_OUT)/tmp
   @echo Copying baseline ramdisk...
-  $(hide) rsync -a --exclude=etc $(TARGET_ROOT_OUT) $(TARGET_RECOVERY_OUT) # "cp -Rf" fails to overwrite broken symlinks on Mac.
+  $(hide) rsync -a --exclude=etc --exclude=sdcard $(TARGET_ROOT_OUT) $(TARGET_RECOVERY_OUT) # "cp -Rf" fails to overwrite broken symlinks on Mac.
   @echo Modifying ramdisk contents...
   $(hide) rm -f $(TARGET_RECOVERY_ROOT_OUT)/init*.rc
   $(hide) cp -f $(recovery_initrc) $(TARGET_RECOVERY_ROOT_OUT)/