xfsdump: remove use of __psint_t, it is no longer available

Commit ee6cd73ed1e in xfsprogs switched __psint_t to the standards
conforming intptr_t type - we need to make the same change here in
xfsdump for builds using the latest xfsprogs headers.

Signed-off-by: Nathan Scott <nathans@debian.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>