scripts: kconfig: merge_config.sh: fix unexpected operator warning

Fix a warning for:

$ ./scripts/kconfig/merge_config.sh .config extra.config
Using .config as base
Merging extra.config
./scripts/kconfig/merge_config.sh: 384: [: false: unexpected operator

The shellcheck report is also attached:

if [ "$STRICT" == "true" ] && [ "$STRICT_MODE_VIOLATED" == "true" ]; then
               ^-- SC3014 (warning): In POSIX sh, == in place of = is undefined.
                                                        ^-- SC3014 (warning): In POSIX sh, == in place of = is undefined.

Fixes: dfc97e1 ("scripts: kconfig: merge_config.sh: use awk in checks too")
Signed-off-by: Weizhao Ouyang <[email protected]>
Reviewed-by: Mikko Rapeli <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Nathan Chancellor <[email protected]>

Author: ownia

scripts/kconfig/merge_config.sh

@@ -381,7 +381,7 @@ END {
 	STRICT_MODE_VIOLATED=true
 fi
 
-if [ "$STRICT" == "true" ] && [ "$STRICT_MODE_VIOLATED" == "true" ]; then
+if [ "$STRICT" = "true" ] && [ "$STRICT_MODE_VIOLATED" = "true" ]; then
 	echo "Requested and effective config differ"
 	exit 1
 fi