nvmem: core: remove global nvmem_cells_group

nvmem_cells_groups is a global variable that is also mutated.
This is complicated and error-prone.

Instead use a normal stack variable.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20240705074852.423202-11-srinivas.kandagatla@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>