tftp: update: Include missing cfi_flash.h header

Add the missing header, otherwise CONFIG_SYS_MAX_FLASH_BANKS
may be undeclared.
Signed-off-by: NMarek Vasut <marek.vasut+renesas@gmail.com>
Cc: Tom Rini <trini@konsulko.com>

common/update.c

@@ -24,6 +24,7 @@
 #include <malloc.h>
 #include <dfu.h>
 #include <errno.h>
+#include <mtd/cfi_flash.h>
 
 /* env variable holding the location of the update file */
 #define UPDATE_FILE_ENV		"updatefile"