package/swupdate: indent with tabs

Commit eb2f2886b2364e5b6a0867f55106bf83acb064e7 ("package/swupdate:
add staging install") has introduced some commands indented with
spaces, which check-package doesn't like.

Fix that by using tabs instead, and while we're at it, wrap the line
that is a bit too long.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/swupdate/swupdate.mk

@@ -230,8 +230,9 @@ define SWUPDATE_BUILD_CMDS
 endef
 
 define SWUPDATE_INSTALL_STAGING_CMDS
-        $(TARGET_MAKE_ENV) $(SWUPDATE_MAKE_ENV) $(MAKE) -C $(@D) \
-                $(SWUPDATE_MAKE_OPTS) DESTDIR=$(STAGING_DIR) INCLUDEDIR=/usr/include/swupdate install
+	$(TARGET_MAKE_ENV) $(SWUPDATE_MAKE_ENV) $(MAKE) -C $(@D) \
+		$(SWUPDATE_MAKE_OPTS) DESTDIR=$(STAGING_DIR) \
+		INCLUDEDIR=/usr/include/swupdate install
 endef
 
 define SWUPDATE_INSTALL_TARGET_CMDS