exfat: Build fsck and update path to mkfs

* Usage of fsck.exfat is already included in partition.cpp, but the
  tool is missing.
* Update the path to mkexfatfs so the button is available when changing
  filesystem.

Change-Id: I5f4e27357c6b5a8606043d1bdc2488cc83e55d90
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index 2160573..068367c 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -128,6 +128,7 @@
 endif
 ifneq ($(TW_NO_EXFAT), true)
     RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/mkexfatfs
+    RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/fsck.exfat
     RELINK_SOURCE_FILES += $(TARGET_OUT_SHARED_LIBRARIES)/libexfat_twrp.so
 else
     TW_NO_EXFAT_FUSE := true