Staging: keucr: Fix externs are avoided in smilsub.c

This patch fixes the following checkpatch.pl warning in smilsub.c-
WARNING: externs should be avoided in .c files

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>