staging: zsmalloc: Ensure handle is never 0 on success

zsmalloc encodes a handle using the pfn and an object
index. On hardware platforms with physical memory starting
at 0x0 the pfn can be 0. This causes the encoded handle to be
0 and is incorrectly interpreted as an allocation failure.

This issue affects all current and future SoCs with physical
memory starting at 0x0. All MSM8974 SoCs which includes
Google Nexus 5 devices are affected.

To prevent this false error we ensure that the encoded handle
will not be 0 when allocation succeeds.

Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>