ubifs: add CONFIG_BLOCK dependency for encryption

This came up during the v4.10 merge window:

warning: (UBIFS_FS_ENCRYPTION) selects FS_ENCRYPTION which has unmet direct dependencies (BLOCK)
fs/crypto/crypto.c: In function 'fscrypt_zeroout_range':
fs/crypto/crypto.c:355:9: error: implicit declaration of function 'bio_alloc';did you mean 'd_alloc'? [-Werror=implicit-function-declaration]
   bio = bio_alloc(GFP_NOWAIT, 1);

The easiest way out is to limit UBIFS_FS_ENCRYPTION to configurations
that also enable BLOCK.

Fixes: d475a507 ("ubifs: Add skeleton for fscrypto")
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NRichard Weinberger <richard@nod.at>

fs/ubifs/Kconfig

@@ -53,7 +53,7 @@ config UBIFS_ATIME_SUPPORT
 
 config UBIFS_FS_ENCRYPTION
 	bool "UBIFS Encryption"
-	depends on UBIFS_FS
+	depends on UBIFS_FS && BLOCK
 	select FS_ENCRYPTION
 	default n
 	help