tools: b43-tools: Update to latest HEAD
Add the following changes:
```
12524df b43-asm: fix undefined behavior by using unsigned shift
fa9cb86 Merge pull request #9 from PolynomialDivision/unsinged-fix
5d592cb fwcutter: Fix compiler warning
b96318b dasm: Fix compiler warning
2270cee ssb_sprom: Fix _DEFAULT_SOURCE warning
4781cde ssb_sprom: Fix compiler warning
cce45e3 ssb_sprom: Update .gitignore
5ca416f disassembler: Update .gitignore
44673b6 Update .gitignore
0c8f8b6 assembler: Update .gitignore
1f5b63d fwcutter: Update .gitignore
35fe438 Add README.md
```
Link: https://github.com/openwrt/openwrt/pull/20542
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>