OMAP: cs should be positive in gpmc_cs_free()

The index `cs' is signed, test whether it is negative before we release
gpmc_cs_mem[cs].

Signed-off-by: Roel Kluin <[e-mail]>
Cc: Russell King <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/arm/mach-omap2/gpmc.c

···
 void gpmc_cs_free(int cs)
 {
 	spin_lock(&gpmc_mem_lock);
-	if (cs >= GPMC_CS_NUM || !gpmc_cs_reserved(cs)) {
+	if (cs >= GPMC_CS_NUM || cs < 0 || !gpmc_cs_reserved(cs)) {
 		printk(KERN_ERR "Trying to free non-reserved GPMC CS%d\n", cs);
 		BUG();
 		spin_unlock(&gpmc_mem_lock);