usb/misc: fix chaoskey build, needs HW_RANDOM

Fix build errors when HW_RANDOM is not enabled:

drivers/built-in.o: In function `chaoskey_disconnect':
chaoskey.c:(.text+0x5f3f00): undefined reference to `hwrng_unregister'
drivers/built-in.o: In function `chaoskey_probe':
chaoskey.c:(.text+0x5f42a6): undefined reference to `hwrng_register'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>