Fix compile time warnings in tc-mips.c

[Nick Clifton]

Hi Maciej,

>  Anyway, thanks for the fix -- I must have not looked for a possible 
> suitable function well enough when implementing these bits. 

If it helps, I ran across this problem whilst building a "mips-ecoff" 
toolchain using a GCC 3.4 based compiler on a 32bit host.

> This should to 2.16 as well if the gate is still open.

Done.

Cheers
   Nick