MdeModulePkg/UdfDxe: Use debug msg instead of ASSERT in UdfOpen()

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1248

Within function UdfOpen():
This commit will use debug messages instead of using ASSERT when an error
occurs after calling GetFileSize().

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Universal/Disk/UdfDxe/File.c

@@ -257,8 +257,12 @@ UdfOpen (
     &NewPrivFileData->File,
     &NewPrivFileData->FileSize
     );
-  ASSERT_EFI_ERROR (Status);
   if (EFI_ERROR (Status)) {
+    DEBUG ((
+      DEBUG_ERROR,
+      "%a: GetFileSize() fails with status - %r.\n",
+      __FUNCTION__, Status
+      ));
     goto Error_Get_File_Size;
   }