tpm: Fix write to file descriptor function

Fix a bug introduced in commit 46f296cd while moving send_all to the
tpm_passthrough code. Fix the name of the variable used in the loop.
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/tpm/tpm_passthrough.c

@@ -86,7 +86,7 @@ static int tpm_passthrough_unix_write(int fd, const uint8_t *buf, uint32_t len)
     int ret, remain;
 
     remain = len;
-    while (len > 0) {
+    while (remain > 0) {
         ret = write(fd, buf, remain);
         if (ret < 0) {
             if (errno != EINTR && errno != EAGAIN) {