fs_mgr: Fix __ANDROID_RECOVERY__ usage in libfiemap.

Certain code in libfiemap should be unreachable in recovery/ramdisk
builds, but whether intentionally or not, __ANDROID_RECOVERY__ is not
working in vendor_boot.

To make sure this is doing exactly what we want, use __ANDROID_RAMDISK__
instead.

Bug: 205987817
Test: build boot, vendor_boot, recovery
Change-Id: Id419f7d9068e791427a896c22569ae4543548df7