exec: replace ffsl with ctzl

See commit fbeadf50 (bitops: unify bitops_ffsl with the one in
host-utils.h, call it bitops_ctzl) on why ctzl should be used instead
of ffsl.

This is also needed for musl libc which does not implement ffsl.
Signed-off-by: NNatanael Copa <ncopa@alpinelinux.org>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

include/exec/ram_addr.h

@@ -117,7 +117,7 @@ static inline void cpu_physical_memory_set_dirty_lebitmap(unsigned long *bitmap,
             if (bitmap[i] != 0) {
                 c = leul_to_cpu(bitmap[i]);
                 do {
-                    j = ffsl(c) - 1;
+                    j = ctzl(c);
                     c &= ~(1ul << j);
                     page_number = (i * HOST_LONG_BITS + j) * hpratio;
                     addr = page_number * TARGET_PAGE_SIZE;