scripts/flashing/flash.sh: Add missing quotes

These are in if statements (where they should be), and echo output that is
not piped to anything. These should be safe.

Found with shellcheck.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

scripts/flashing/flash.sh

@@ -20,8 +20,8 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 #
 
-if [ -z "$1" ] || [ ! -f $1 ] || [ -z $2 ]; then
-    echo Usage: $0 firmware vendor
+if [ -z "$1" ] || [ ! -f "$1" ] || [ -z "$2" ]; then
+    echo Usage: "$0" firmware vendor
 cat << EOF
 IMPORTANT:
 Notes for Linksys / Asus WL500gx router: 
@@ -52,15 +52,15 @@ fi
 if [ "$2" = "asus" ]; then
 echo Confirming IP address setting...
 echo -en "get ASUSSPACELINK\x01\x01\xa8\xc0 /dev/null\nquit\n" | tftp 192.168.1.1
-echo Flashing 192.168.1.1 using $1...
+echo Flashing 192.168.1.1 using "$1"...
 echo -en "binary\nput $1 ASUSSPACELINK\nquit\n" | tftp 192.168.1.1
 echo Please wait until leds stops flashing. 
 elif [ "$2" = "linksys" ]; then
-echo Flashing 192.168.1.1 using $1...
+echo Flashing 192.168.1.1 using "$1"...
 echo -en "rexmt 1\ntrace\nbinary\nput $1\nquit\n" | tftp 192.168.1.1
 echo Please wait until power led stops flashing. Do not poweroff! Then you can login via telnet 192.168.1.1.
 elif [ "$2" = "toshiba" ]; then
-echo Flashing 192.168.10.1 using $1...
+echo Flashing 192.168.10.1 using "$1"...
 echo -en "rexmt 1\ntrace\nbinary\nput $1\nquit\n" | tftp 192.168.10.1
 echo Unit will automatically reboot within 5 minutes.  Do not power off.  Then you can login via telnet 192.168.10.1.
 fi