botan: fix install directory

Using $(STAGING_DIR)/usr and $(TARGET_DIR)/usr as the DESTDIR value
causes Botan to be installed in $(STAGING_DIR)/usr/usr and
$(TARGET_DIR)/usr/usr, which obviously isn't correct. Let's fix that
by passing the appropriate DESTDIR values.

Signed-off-by: DUPONCHEEL Sébastien <sebastien.duponcheel@corp.ovh.com>
[Thomas: extend commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/botan/botan.mk

@@ -92,11 +92,11 @@ define BOTAN_BUILD_CMDS
 endef
 
 define BOTAN_INSTALL_STAGING_CMDS
-	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) DESTDIR="$(STAGING_DIR)/usr" install
+	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) DESTDIR="$(STAGING_DIR)" install
 endef
 
 define BOTAN_INSTALL_TARGET_CMDS
-	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) DESTDIR="$(TARGET_DIR)/usr" install
+	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) DESTDIR="$(TARGET_DIR)" install
 endef
 
 $(eval $(generic-package))