fmlib: use $(TARGET_MAKE_ENV) when calling $(MAKE)

And drop FMLIB_MAKE_ENV which is non-existant as pointed by Arnout.

Signed-off-by: Gustavo Zacarias <gustavo.zacarias@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/fmlib/fmlib.mk

@@ -31,7 +31,7 @@ endef
 
 define FMLIB_INSTALL_STAGING_CMDS
 	$(RM) $(STAGING_DIR)/usr/lib/libfm.a
-	$(FMLIB_MAKE_ENV) $(MAKE) $(FMLIB_MAKE_OPTS) -C $(@D) install-libfm-$(FMLIB_ARCHTYPE)
+	$(TARGET_MAKE_ENV) $(MAKE) $(FMLIB_MAKE_OPTS) -C $(@D) install-libfm-$(FMLIB_ARCHTYPE)
 endef
 
 $(eval $(generic-package))