platform/mellanox: mlxreg-lc: Fix coverity warning

platform/mellanox: mlxreg-lc: Fix coverity warning

Fix smatch warning:
drivers/platform/mellanox/mlxreg-lc.c:866 mlxreg_lc_probe() warn: passing zero to 'PTR_ERR'
by removing 'err = PTR_ERR(regmap)'.

Fixes: a266b9963586 ("platform/mellanox: mlxreg-lc: Fix error flow and extend verbosity")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20220823201937.46855-2-vadimp@nvidia.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>