Blackfin arch: Fix bug using usb keyboard crashes kernel

Blackfin arch: Fix bug using usb keyboard crashes kernel

Without conswitchp preset, we have the following situation:

 - During initcalls: con_init is called, and returns because of
   !display_desc.

 - At this point there is no memory allocated for vc_cons[].d
   A bit later vty_init calls kbd_init.

 - From now on events are passed to kbd_event which will then call
   kbd_keycode.

 - kbd_keycode will oops on a NULL pointer dereference on vc->vc_tty

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
[ Added commit description based on email thread. - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>