MdeModulePkg/UdfDxe: replace zero-init of local variables with ZeroMem()

MdeModulePkg/UdfDxe: replace zero-init of local variables with ZeroMem()

In edk2, initialization of local variables is forbidden, both for
stylistic reasons and because such initialization may generate calls to
compiler intrinsics.

For the following initialization in UdfRead():

  CHAR16                          FileName[UDF_FILENAME_LENGTH] = { 0 };

clang-3.8 generates a memset() call, when building UdfDxe for IA32, which
then fails to link.

Replace the initialization with ZeroMem().

Do the same to "FilePath" in UdfOpen().

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Paulo Alcantara <pcacjr@zytor.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Paulo Alcantara <pcacjr@zytor.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>