fix CPU_ISSET signature for freebsd/dragonflybsd.

indeed no rason to be mutable and to match linux part as well.

Author: devnexen

src/unix/bsd/freebsdlike/dragonfly/mod.rs

@@ -1335,7 +1335,7 @@ f! {
         ()
     }
 
-    pub fn CPU_ISSET(cpu: usize, cpuset: &mut cpu_set_t) -> bool {
+    pub fn CPU_ISSET(cpu: usize, cpuset: &cpu_set_t) -> bool {
         let (idx, offset) = ((cpu >> 6) & 3, cpu & 63);
         0 != cpuset.ary[idx] & (1 << offset)
     }

src/unix/bsd/freebsdlike/freebsd/mod.rs

@@ -1528,7 +1528,7 @@ f! {
         ()
     }
 
-    pub fn CPU_ISSET(cpu: usize, cpuset: &mut cpuset_t) -> bool {
+    pub fn CPU_ISSET(cpu: usize, cpuset: &cpuset_t) -> bool {
         let bitset_bits = ::mem::size_of::<::c_long>();
         let (idx, offset) = (cpu / bitset_bits, cpu % bitset_bits);
         0 != cpuset.__bits[idx] & (1 << offset)