[PARTMGR] Fix x64 build warning

warning C4267: 'function': conversion from 'size_t' to 'ULONG', possible loss of data'

The OutputBufferLength member that was temporarily stored in
outBufferLength is already a ULONG, and IssueSyncIoControlRequest()
takes the length as a ULONG. So there is no need to use 'size_t' here.

drivers/storage/partmgr/partmgr.c

@@ -367,7 +367,7 @@ FdoIoctlDiskGetDriveGeometryEx(
  // as disk.sys doesn't really know about the partition table on a disk
 
  PDISK_GEOMETRY_EX_INTERNAL geometryEx = Irp->AssociatedIrp.SystemBuffer;
- size_t outBufferLength = ioStack->Parameters.DeviceIoControl.OutputBufferLength;
+ ULONG outBufferLength = ioStack->Parameters.DeviceIoControl.OutputBufferLength;
  NTSTATUS status;
 
  status = IssueSyncIoControlRequest(IOCTL_DISK_GET_DRIVE_GEOMETRY_EX,