uboot-imx

Fix checking fat32 cluster size.

This fixes the cluster size tests in the FAT32 file system.
The current implementation of VFAT support doesn't work if the
referred cluster has an offset > 16bit representation, causing
"fatload" and "fatls" commands etc. to fail.

Signed-off-by: michael trimarchi <trimarchi@gandalf.sssup.it>