tools: b43-tools: fix compilation with GCC14

tools: b43-tools: fix compilation with GCC14

GCC14 no longer treats integer types and pointer types as equivalent in
assignments (including implied assignments of function arguments and return
values), and instead fails the compilation with a type error.

So, as a workaround lets disable the newly introduced error
-Werror=int-conversion and just make it print a warning to enable compiling
with GCC14 as Fedora 40 now defaults to it.

(cherry picked from commit 0c96d20bf9fba6d814efa88c6fb08a5df094103a)
Link: https://github.com/openwrt/openwrt/pull/15309
Signed-off-by: Robert Marko <robimarko@gmail.com>