bitbake: bitbake: fix typo in variable name

When passing -t with an incorrect server type, the error message was using a
variable that doesn't exist.

(Bitbake rev: 98b991287df06cd89955c1d0591fce3b5d4403d1)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake

@@ -259,7 +259,7 @@ def main():
         servermodule = getattr(module, server_type)
     except AttributeError:
         sys.exit("FATAL: Invalid server type '%s' specified.\n"
-                 "Valid interfaces: xmlrpc, process [default]." % servertype)
+                 "Valid interfaces: xmlrpc, process [default]." % server_type)
 
     if configParams.server_only:
         if configParams.servertype != "xmlrpc":