omap_intc: convert ffs(3) to ctz32() in omap_inth_sir_update()

Rewrite the loop using level &= level - 1 to clear the least significant
bit after each iteration.  This simplifies the loop and makes it easy to
replace ffs(3) with ctz32().

Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427124571-28598-8-git-send-email-stefanha@redhat.com
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

hw/intc/omap_intc.c

@@ -60,7 +60,7 @@ struct omap_intr_handler_s {
 
 static void omap_inth_sir_update(struct omap_intr_handler_s *s, int is_fiq)
 {
-    int i, j, sir_intr, p_intr, p, f;
+    int i, j, sir_intr, p_intr, p;
     uint32_t level;
     sir_intr = 0;
     p_intr = 255;
@@ -72,14 +72,15 @@ static void omap_inth_sir_update(struct omap_intr_handler_s *s, int is_fiq)
     for (j = 0; j < s->nbanks; ++j) {
         level = s->bank[j].irqs & ~s->bank[j].mask &
                 (is_fiq ? s->bank[j].fiq : ~s->bank[j].fiq);
-        for (f = ffs(level), i = f - 1, level >>= f - 1; f; i += f,
-                        level >>= f) {
+
+        while (level != 0) {
+            i = ctz32(level);
             p = s->bank[j].priority[i];
             if (p <= p_intr) {
                 p_intr = p;
                 sir_intr = 32 * j + i;
             }
-            f = ffs(level >> 1);
+            level &= level - 1;
         }
     }
     s->sir_intr[is_fiq] = sir_intr;