Staging: octeon: Remove extern from .c file

This patch fixes the checkpatch.pl warning:

WARNING: externs should be avoided in .c files
+extern void octeon_mdiobus_force_mod_depencency(void);

Signed-off-by: Helen Fornazier <helen.fornazier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>