driver core: fix up missed drivers/s390/char/hmcdrv_dev.c class.devnode() conversion.

Fixes: ff62b8e6 ("driver core: make struct class.devnode() take a const *")
Link: https://lore.kernel.org/r/20221130123851.6a9f2242@canb.auug.org.au


Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>