cyber2000fb.c: use proper method for stopping unload if CONFIG_ARCH_SHARK

Russell explains the __module_get():
> cyber2000fb.c does it in its module initialization function
> to prevent the module (when built for Shark) from being unloaded.  It
> does this because it's from the days of 2.2 kernels and no one bothered
> writing the module unload support for Shark.

Since 2.4, the correct answer has been to not define an unload fn.

Cc: Russell King <rmk+lkml@arm.linux.org.uk>
Cc: alex@shark-linux.de
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>