debug: symtab: fix ignored type qualifiers on func return type

[XenuIsWatching]

const is ignored on the function return type. A warning is reported with -Wignored-qualifers. Remove the ignored qualifier.

In file included from zephyr/subsys/shell/modules/kernel_service.c:27:
zephyr/include/zephyr/debug/symtab.h:49:1: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
   49 | const struct symtab_info *const symtab_get(void);
      | ^~~~~
zephyr/include/zephyr/debug/symtab.h:60:1: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
   60 | const char *const symtab_find_symbol_name(uintptr_t addr, uint32_t *offset);
      | ^~~~~

[ycsin]

As noted by @dcpleung, updating the function return type should fix the compilation warnings, could you update the patch please?

[ycsin]

LGTM