Fix the inconsistency in x509-dh-key-file parameter

Commit c448e855 (spice: tls
support) added options to the -spice command line. But there
is an inconsistency between the declaration of the option
'x509-dh-key-file' to -spice command line and its parameter
parsing 'x509-dh-file' in function qemu_spice_init.

https://bugs.launchpad.net/qemu/+bug/1035042Reported-by: NAlon Bar-Lev <alon.barlev@gmail.com>
Signed-off-by: NLei Li <lilei@linux.vnet.ibm.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

ui/spice-core.c

@@ -610,7 +610,7 @@ void qemu_spice_init(void)
         }
 
         x509_key_password = qemu_opt_get(opts, "x509-key-password");
-        x509_dh_file = qemu_opt_get(opts, "x509-dh-file");
+        x509_dh_file = qemu_opt_get(opts, "x509-dh-key-file");
         tls_ciphers = qemu_opt_get(opts, "tls-ciphers");
     }