nvmem: qcom-spmi-sdam: Enable multiple devices

Specifying the name of the nvmem device while registering it with the
nvmem framework has the side effect of causing the second instance of a
device using this driver to fail probe with the following error message:

  sysfs: cannot create duplicate filename '/bus/nvmem/devices/spmi_sdam'

Removing the name allows the nvmem framework to assign a monotonically
increasing integer id to each instance of this driver automatically,
like so:

  /sys/bus/nvmem/devices # ls
  nvmem0  nvmem1  nvmem2

Change-Id: I15acfad796babc4019cb0e6aa5ac4b880ce10f3e
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>