rng-egd: offset the point when repeatedly read from the buffer

The buffer content might be read out more than once, currently
we just repeatedly read the first data block, buffer offset is
missing.

Cc: qemu-stable@nongnu.org
Signed-off-by: NAmos Kong <akong@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

backends/rng-egd.c

@@ -91,12 +91,14 @@ static int rng_egd_chr_can_read(void *opaque)
 static void rng_egd_chr_read(void *opaque, const uint8_t *buf, int size)
 {
     RngEgd *s = RNG_EGD(opaque);
+    size_t buf_offset = 0;
 
     while (size > 0 && s->requests) {
         RngRequest *req = s->requests->data;
         int len = MIN(size, req->size - req->offset);
 
-        memcpy(req->data + req->offset, buf, len);
+        memcpy(req->data + req->offset, buf + buf_offset, len);
+        buf_offset += len;
         req->offset += len;
         size -= len;