driver core: class.h: remove extern from function prototypes

The kernel coding style does not require 'extern' in function prototypes
in .h files, so remove them from include/linux/device/class.h as they
are not needed.

Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20230324100132.1633647-2-gregkh@linuxfoundation.org


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