wimax: fix '#ifndef CONFIG_BUG' layout to avoid warning

Reported by Randy Dunlap:

> Also, this warning needs to be fixed:
>
> linux-next-20090106/net/wimax/id-table.c:133: warning: ISO C90
> forbids mixed declarations and code

Move the return on #defined(CONFIG_BUG) below the variable
declarations so it doesn't violate ISO C90.

On wimax_id_table_release() we want to do a debug check if CONFIG_BUG
is enabled. However, we also want the debug code to be always compiled
to ensure there is no bitrot. It will be optimized out by the compiler
when CONFIG_BUG is disabled.

Added a note to the function header stating this.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>