noip: use a simpler sed command with our $(SED) variable

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/noip/noip.mk

@@ -11,8 +11,7 @@ NOIP_LICENSE = GPLv2+
 NOIP_LICENSE_FILES = COPYING
 
 define NOIP_BUILD_CMDS
-	sed -i -e "s:\(#define CONFIG_FILENAME\).*:\1 \"/etc/no-ip2.conf\":" \
-		$(@D)/noip2.c
+	$(SED) "/^#define CONFIG_FILENAME/ s/PREFIX//" $(@D)/noip2.c
 	$(MAKE) -C $(@D) CC="$(TARGET_CC)" CFLAGS="$(TARGET_CFLAGS)" \
 		PREFIX=/usr CONFDIR=/etc
 endef