platform/mellanox: mlxreg-hotplug: Remove redundant NULL-check

platform/mellanox: mlxreg-hotplug: Remove redundant NULL-check

Pointer item is checked fo NULL at mlxreg_hotplug_work_helper() and then
it is dereferenced to produce dev_err().
This pointer is also dereferenced before calling this function and should
never be NULL except some piece of hardware is broken as it is said in
the comment before the check. So, this check can be safely removed.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: c6acad68eb2d ("platform/mellanox: mlxreg-hotplug: Modify to use a regmap interface")
Signed-off-by: Daniil Dulov <d.dulov@aladdin.ru>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20240306153804.6509-1-d.dulov@aladdin.ru
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>