MdeModulePkg: NvmExpressDxe: fix warning about uninitialized variable

NvmExpressMediaSanitize.c: In function 'NvmExpressMediaClear':
NvmExpressMediaSanitize.c:337:29: error: 'Status' may be used uninitialized
  in this function [-Werror=maybe-uninitialized]

   EFI_STATUS                Status;
                             ^~~~~~
cc1: all warnings being treated as errors

Signed-off-by: Mike Maslenkin <mike.maslenkin@gmail.com>

MdeModulePkg/Bus/Pci/NvmExpressDxe/NvmExpressMediaSanitize.c

@@ -360,6 +360,8 @@ NvmExpressMediaClear (
     return EFI_INVALID_PARAMETER;
   }
 
+  Status = EFI_SUCCESS;
+
   //
   // Per NIST 800-88r1, one or more pass of writes may be alteratively used.
   //