docs: nvmem: remove function parameters (fixes hyperlink generation)

Adding a parameter is not particularly useful here, and it is definitely
not done elsewhere. It also prevents the generation of a hyperlink to the
kernel-doc documentation. Removing the parameter to enable hyperlinks and
make the style coherent.
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231201-nvmem-docs-kerneldoc-v1-2-3e8f2b706ce6@bootlin.com

Documentation/driver-api/nvmem.rst

@@ -41,7 +41,7 @@ A NVMEM provider can register with NVMEM core by supplying relevant
 nvmem configuration to nvmem_register(), on success core would return a valid
 nvmem_device pointer.
 
-nvmem_unregister(nvmem) is used to unregister a previously registered provider.
+nvmem_unregister() is used to unregister a previously registered provider.
 
 For example, a simple nvram case::