[LibOS] Fix ret variable shadowing in clear_pollable_event()

There was a typo that accidentally declared `int ret` in a while-loop
scope and thus shadowed the `ret` variable in the function scope. This
led to the bogus loop (it would always execute only once).

Signed-off-by: jkr0103 <jitender.kumar@intel.com>

libos/src/libos_pollable_event.c

@@ -97,7 +97,7 @@ int clear_pollable_event(struct libos_pollable_event* event) {
     do {
         char buf[0x100];
         size_t size = sizeof(buf);
-        int ret = PalStreamRead(event->read_handle, /*offset=*/0, &size, buf);
+        ret = PalStreamRead(event->read_handle, /*offset=*/0, &size, buf);
         ret = pal_to_unix_errno(ret);
         if (ret == 0 && size == 0) {
             ret = -EINVAL;