ArmVirtPkg: use explicit KERNEL_BLOB_TYPE cast

ArmVirtPkg: use explicit KERNEL_BLOB_TYPE cast

The ARM RVCT compiler does not allow implicit casts between enumerated
types and integer types. In this particular case, the STUB_FILE::Position
member is overloaded as a KERNEL_BLOB_TYPE identifier, so it does not
hurt to make that cast explicit.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19108 6f19259b-4bc3-4df7-8a09-765794883524