add registers to sqrt clobber list

will need to go through the other syscalls and find out whether we need
to add registers to the clobber list. We probably need to add all per
the call convention (r0, r1, r2, r3 are callee saved).

agb/src/syscall.rs

@@ -77,6 +77,9 @@ pub fn sqrt(n: i32) -> i32 {
             "swi 0x08",
             in("r0") n,
             lateout("r0") result,
+            lateout("r1") _,
+            lateout("r2") _,
+            lateout("r3") _
         );
     }
     result
@@ -102,6 +105,7 @@ pub fn arc_tan2(x: i16, y: i32) -> i16 {
             in("r0") x,
             in("r1") y,
             lateout("r0") result,
+
         );
     }
     result