Revert "loop: Remove sector_t truncation checks"

This reverts commit f92a3b0d, which
was commit 083a6a50783ef54256eec3499e6575237e0e3d53 upstream.  In 4.19
there is still an option to use 32-bit sector_t on 32-bit
architectures, so we need to keep checking for truncation.

Since loop_set_status() was refactored by subsequent patches, this
reintroduces its truncation check in loop_set_status_from_info()
instead.

I tested that the loop ioctl operations have the expected behaviour on
x86_64, x86_32 with CONFIG_LBDAF=y, and (the special case) x86_32 with
CONFIG_LBDAF=n.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>