scripts/qemu-binfmt-conf.sh: Fix shell portability issue

Appease pkgsrc and use portable shell variable comparison.
This switches "==" to "=". It should not be a functional change.

Signed-off-by: Kamil Rytarowski <n54@gmx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

scripts/qemu-binfmt-conf.sh

@@ -284,12 +284,12 @@ while true ; do
         shift
         # check given cpu is in the supported CPU list
         for cpu in ${qemu_target_list} ; do
-            if [ "$cpu" == "$1" ] ; then
+            if [ "$cpu" = "$1" ] ; then
                 break
             fi
         done
 
-        if [ "$cpu" == "$1" ] ; then
+        if [ "$cpu" = "$1" ] ; then
             qemu_target_list="$1"
         else
             echo "ERROR: unknown CPU \"$1\"" 1>&2