fs/fat: Reduce stack usage

We have limited stack in SPL builds.  Drop itrblock and move to
malloc/free of itr to move this off of the stack.  As part of this fix a
double-free issue in fat_size().

Signed-off-by: Tom Rini <trini@konsulko.com>
---
Rework to use malloc/free as moving this to a global overflows some SH
targets.
1 file changed