platform/mellanox: mlxreg-hotplug: Fix uninitialized variable

With gcc-4.1.2:

    drivers/platform/mellanox/mlxreg-hotplug.c: In function ‘mlxreg_hotplug_health_work_helper’:
    drivers/platform/mellanox/mlxreg-hotplug.c:347: warning: ‘ret’ is used uninitialized in this function

Indeed, if mlxreg_core_item.count is zero, ret is used uninitialized.

While this is unlikely to happen (it is set to ARRAY_SIZE(...) in x86
board files), this is done in another source file, so fix this by
preinitializing ret to zero.

Fixes: c6acad68 ("platform/mellanox: mlxreg-hotplug: Modify to use a regmap interface")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>