scripts: kconfig: merge_config.sh: fix indentation

Replace spaces with tabs for consistency with the rest of the script.

Fixes: 5fa9b82c ("scripts: kconfig: merge_config.sh: refactor from shell/sed/grep to awk")
Signed-off-by: Daniel Gomez <da.gomez@samsung.com>
Link: https://patch.msgid.link/20260310-fixes-merge-config-v1-2-beaeeaded6bd@samsung.com


Signed-off-by: Nathan Chancellor <nathan@kernel.org>