[netdrvr] natsemi: Fix device removal bug

This episode illustrates how an overused warning can train people to
ignore that warning, which winds up hiding bugs.

The warning

drivers/net/natsemi.c: In function ‘natsemi_remove1’:
drivers/net/natsemi.c:3222: warning: ignoring return value of
‘device_create_file’, declared with attribute warn_unused_result

is oft-ignored, even though at close inspection one notices this occurs
in the /remove/ function, not normally where creation occurs.  A quick
s/create/remove/ and we are fixed, with the warning gone.

Signed-off-by: Jeff Garzik <jeff@garzik.org>