[SPARC64]: of_device_register() error checking fix

device_create_file() can fail.  This causes the sparc64 compile to
fail when my fanatical __must_check patch is applied, due to -Werror.

[ Added necessary identical fix for sparc32. -DaveM]

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>