mtd: nandsim: Staticize local symbols

These local symbols are used only in this file.
Fix the following sparse warnings:

drivers/mtd/nand/nandsim.c:1436:5: warning: symbol 'do_read_error' was not declared. Should it be static?
drivers/mtd/nand/nandsim.c:1448:6: warning: symbol 'do_bit_flips' was not declared. Should it be static?
Signed-off-by: NJingoo Han <jg1.han@samsung.com>
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/nand/nandsim.c

@@ -1433,7 +1433,7 @@ static inline u_char *NS_PAGE_BYTE_OFF(struct nandsim *ns)
 	return NS_GET_PAGE(ns)->byte + ns->regs.column + ns->regs.off;
 }
 
-int do_read_error(struct nandsim *ns, int num)
+static int do_read_error(struct nandsim *ns, int num)
 {
 	unsigned int page_no = ns->regs.row;
 
@@ -1445,7 +1445,7 @@ int do_read_error(struct nandsim *ns, int num)
 	return 0;
 }
 
-void do_bit_flips(struct nandsim *ns, int num)
+static void do_bit_flips(struct nandsim *ns, int num)
 {
 	if (bitflips && prandom_u32() < (1 << 22)) {
 		int flips = 1;