BaseTools:Coding problems cause can not encode FMP Auth Header

GenerateCapsule: error: can not encode FMP Auth Header
The system cannot find the file specified.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>

BaseTools/Source/Python/Capsule/GenerateCapsule.py

@@ -126,7 +126,7 @@ def SignPayloadOpenSsl (Payload, ToolPath, SignerPrivateCertFile, OtherPublicCer
     try:
         Process = subprocess.Popen (Command, stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE, shell = True)
         Result = Process.communicate(input = Payload)
-        Signature = Result[0].decode(encoding='utf-8', errors='ignore')
+        Signature = Result[0]
     except:
         raise ValueError ('GenerateCapsule: error: can not run openssl.')