file: select zlib

file depends on zlib, so make it visible in kconfig.

package/file/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_FILE
 	bool "file"
+	select BR2_PACKAGE_ZLIB
 	help
 	  Program to identify a file's format by scanning binary data
 	  for known patterns.