zsmalloc: replace IS_ERR() with IS_ERR_VALUE()

Avoid typecasts that are needed for IS_ERR() and use IS_ERR_VALUE()
instead.

Link: https://lkml.kernel.org/r/20221104023818.1728-1-wangdeming@inspur.com


Signed-off-by: Deming Wang <wangdeming@inspur.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>