openpower/libflash: Correctly install to target

Fix a copy/paste error that results in libflash.so being installed to
staging instead of the target directory.

Signed-off-by: Sam Mendoza-Jonas <sam@mendozajonas.com>
diff --git a/openpower/package/libflash/libflash.mk b/openpower/package/libflash/libflash.mk
index 5c6e393..f39e8c8 100644
--- a/openpower/package/libflash/libflash.mk
+++ b/openpower/package/libflash/libflash.mk
@@ -28,7 +28,7 @@
 endef
 
 define LIBFLASH_INSTALL_TARGET_CMDS
-	PREFIX=$(STAGING_DIR)/usr SKIBOOT_VERSION=$(LIBFLASH_VERSION) \
+	PREFIX=$(TARGET_DIR)/usr SKIBOOT_VERSION=$(LIBFLASH_VERSION) \
 	       $(MAKE1) $(LIBFLASH_MAKE_OPTS) CROSS_COMPILE=$(TARGET_CROSS) \
 	       -C $(@D)/external/shared install-lib
 endef