uboot-lantiq: fix C-style comments in AWK scripts

uboot-lantiq: fix C-style comments in AWK scripts

Modern gawk rejects C-style /* ... */ comments in AWK code, treating
them as regex patterns where '*' has nothing to quantify. Replace all
such comments with AWK-style '#' comments in lantiq_bdi_conf.awk and
lantiq_ram_init_uart.awk.

Also replace the pattern 'if (x) /* comment */ else action' which used
a C comment as a null statement with the equivalent 'if (!x) action'.

Fixes build error:
  awk: error: ? * + or {interval} not preceded by valid subpattern

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Link: https://github.com/openwrt/openwrt/pull/22458
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>