- Mark temp variable as "earlyclobber" in assembler inline in

atomic_fetchadd_32.  Without it gcc would use it as input
    register for v and sometimes generate following code for
    function call like atomic_fetchadd_32(&(fp)->f_count, -1):

801238b4:       2402ffff        li      v0,-1
801238b8:       c2230018        ll      v1,24(s1)
801238bc:       00431021        addu    v0,v0,v1
801238c0:       e2220018        sc      v0,24(s1)
801238c4:       1040fffc        beqz    v0,801238b8 <dupfdopen+0x2e8>
801238c8:       00000000        nop

   Which is definitly wrong because if sc fails v0 is set to 0
   and previous value of -1 is overriden hence whole operation
   turns to bogus

sys/mips/include/atomic.h

@@ -294,7 +294,7 @@ atomic_fetchadd_32(__volatile uint32_t *p, uint32_t v)
 		"addu %2, %3, %0\n\t"		/* calculate new value */
 		"sc %2, %1\n\t"			/* attempt to store */
 		"beqz %2, 1b\n\t"		/* spin if failed */
-		: "=&r" (value), "=m" (*p), "=r" (temp)
+		: "=&r" (value), "=m" (*p), "=&r" (temp)
 		: "r" (v), "m" (*p));
 	return (value);
 }