static: keucr: Fix sparse warning of static declarations

This patch fixes the warning:
drivers/staging/keucr/smilsub.c:603:6: warning: symbol '_Check_D_DevCode' was not declared. Should it be static?
by making function static as it is used within the file.

Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Acked-by: Pablo Neira Ayuso <pablo@gnumonks.org>
Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>