utils/config: fix shellcheck errors

SC2086 is now reported for missing Double quote around
$FN since shellcheck 0.9.0:

In utils/config line 175:
                if grep -q "# ${BR2_PREFIX}$ARG is not set" $FN ; then
                                                            ^-^ SC2086 (info): Double quote to prevent globbing and word splitting.

In utils/config line 178:
                        if V="$(grep "^${BR2_PREFIX}$ARG=" $FN)"; then
                                                           ^-^ SC2086 (info): Double quote to prevent globbing and word splitting.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

utils/config

@@ -172,10 +172,10 @@ while [ "$1" != "" ] ; do
 		;;
 
 	--state|-s)
-		if grep -q "# ${BR2_PREFIX}$ARG is not set" $FN ; then
+		if grep -q "# ${BR2_PREFIX}$ARG is not set" "$FN" ; then
 			echo n
 		else
-			if V="$(grep "^${BR2_PREFIX}$ARG=" $FN)"; then
+			if V="$(grep "^${BR2_PREFIX}$ARG=" "$FN")"; then
 				V="${V/#${BR2_PREFIX}$ARG=/}"
 				V="${V/#\"/}"
 				V="${V/%\"/}"