mtd: cfi_flash: fix clang warning

clang warns this check is silly; it is since s is
a local variable.

u-boot/drivers/mtd/cfi_flash.c:2363:13: warning: comparison of
  array 's' not equal to a null pointer is always true
  else if ((s != NULL) && (strcmp(s, "yes") == 0)) {

cc: Stefan Roese <sr@denx.de>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>

drivers/mtd/cfi_flash.c

@@ -2360,7 +2360,7 @@ unsigned long flash_init (void)
 #endif /* CONFIG_SYS_FLASH_QUIET_TEST */
 		}
 #ifdef CONFIG_SYS_FLASH_PROTECTION
-		else if ((s != NULL) && (strcmp(s, "yes") == 0)) {
+		else if (strcmp(s, "yes") == 0) {
 			/*
 			 * Only the U-Boot image and it's environment
 			 * is protected, all other sectors are