qemu-img: Remove redundancy "ret = -1"

In this case, 'ret' is already '-1', so need not do it again.
Signed-off-by: NChen Gang <gang.chen.5i5j@gmail.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

qemu-img.c

@@ -246,7 +246,6 @@ static int read_password(char *buf, int buf_size)
             if (errno == EAGAIN || errno == EINTR) {
                 continue;
             } else {
-                ret = -1;
                 break;
             }
         } else if (ret == 0) {