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>

drivers/staging/keucr/smilsub.c

@@ -600,7 +600,7 @@ int Set_D_SsfdcModel(BYTE dcode)
 }
 
 /* ----- _Check_D_DevCode() --------------------------------------------- */
-BYTE _Check_D_DevCode(BYTE dcode)
+static BYTE _Check_D_DevCode(BYTE dcode)
 {
 	switch (dcode) {
 	case 0x6E: