preinit: use grep -q where applicable

SVN-Revision: 19484

target/linux/pxcab/base-files/lib/preinit/45_failsafe_pxcab

@@ -4,7 +4,7 @@
 
 failsafe_wait() {
     FAILSAFE=
-    grep 'failsafe=' /proc/cmdline > /dev/null && FAILSAFE=true && export FAILSAFE
+    grep -q 'failsafe=' /proc/cmdline && FAILSAFE=true && export FAILSAFE
     if [ "$FAILSAFE" != "true" ]; then
         preinit_net_echo "Please press button now to enter failsafe"
         echo -n "Press "