staging: silicom: fix sparse warning for static variable

This patch fixes the following sparse warning in bpctl_mod.c:
warning: symbol 'bpvm_lock' was not declared. Should it be static?
Signed-off-by: NJames A Shackleford <shack@linux.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/silicom/bpctl_mod.c

@@ -41,7 +41,7 @@ MODULE_AUTHOR("Anna Lukin, annal@silicom.co.il");
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION(BP_MOD_DESCR);
 MODULE_VERSION(BP_MOD_VER);
-spinlock_t bpvm_lock;
+static spinlock_t bpvm_lock;
 
 #define unlock_bpctl()					\
 	up(&bpctl_sema);