OvmfPkg/BaseMemEncryptSevLib: clean up DEBUG prefixes

OvmfPkg/BaseMemEncryptSevLib: clean up DEBUG prefixes

The prefix for the SetMemoryEncDec() DEBUG messages should be

  "ModuleName:FunctionName: "

not

  "ModuleName:FunctionName "

Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
Tested-by: Brijesh Singh <brijesh.singh@amd.com>