staging/zcache: don't use PTR_RET().
staging/zcache: don't use PTR_RET().

We've already tested that it's an error.

Cc: Dan Magenheimer <017adcb67eaa7bc3974e87882304023d2fcc0db7@oracle.com>
Signed-off-by: Rusty Russell <df9728c9e5104131c08c7adb03af425394842596@rustcorp.com.au>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs