iwl3945: do not print RFKILL message

We can mess logs if user space try to open device again and again if
RFKILL switch is on. Do not print message and return ERFKILL error
instead to indicate where the problem is.

Note that iwl4965 handle this problem differently, it allows to open
device when radio is disabled.

Reported-by: Dietmar Rudolph <dietmar@crlf.de>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>