comedi: comedi_8254: Replace comedi_8254_init() and comedi_8254_mm_init()

comedi: comedi_8254: Replace comedi_8254_init() and comedi_8254_mm_init()

`comedi_8254_init()` and `comedi_8254_mm_init()` return `NULL` on
failure, but the failure is not necessarily due to lack of memory.
Change them to return an `ERR_PTR` value on failure and rename the
functions to make it obvious the API has changed.  `comedi_8254_init()`
has been replaced with `comedi_8254_io_alloc()`, and
`comedi_8254_mm_init()` has been replaced with `comedi_8254_mm_alloc()`.

Cc: Arnd Bergmann <arnd@kernel.org>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20230913170712.111719-4-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>