OvmfPkg: VirtioScsiDxe: drop 64-bit shift in PopulateRequest() (VS2010)

"Lun" has type UINT64 in this function. The result of the expression

  (UINT8) ((Lun >> 8) | 0x40)

depends only on bits [15:8] of "Lun", therefore we can cast "Lun" to
UINT32 before shifting it.

This eliminates an intrinsic when building with VS2010 for Ia32 / NOOPT.

Contributed-under: TianoCore Contribution Agreement 1.0

Signed-off-by: Scott Duplichan <scott@notabs.org>

[lersek@redhat.com: added commit message]

Signed-off-by: Laszlo Ersek <lersek@redhat.com>

Build-tested-by: Scott Duplichan <scott@notabs.org>

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16386 6f19259b-4bc3-4df7-8a09-765794883524