nvmem: update a comment related to struct nvmem_config

Update a comment to match the function used in nvmem_register(). 
ida_simple_get() was replaced by ida_alloc() in commit 1eb51d6a
("nvmem: switch to simpler IDA interface")

Link: https://lkml.kernel.org/r/27a9dec93a9f79140b11a77df38b1b45bd342e09.1752480043.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>