pstore: fix crypto dependencies without compression

Commit 58eb5b6707 ("pstore: fix crypto dependencies") fixed up the crypto
dependencies but missed the case when no compression is selected.

With CONFIG_PSTORE=y, CONFIG_PSTORE_COMPRESS=n  and CONFIG_CRYPTO=m we see
the following link error:

fs/pstore/platform.o: In function `pstore_register':
(.text+0x1b1): undefined reference to `crypto_has_alg'
(.text+0x205): undefined reference to `crypto_alloc_base'
fs/pstore/platform.o: In function `pstore_unregister':
(.text+0x3b0): undefined reference to `crypto_destroy_tfm'

Fix this by checking at compile-time if CONFIG_PSTORE_COMPRESS is enabled.

Fixes: 58eb5b6707 ("pstore: fix crypto dependencies")
Signed-off-by: Tobias Regnery <tobias.regnery@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/platform.c

@@ -258,7 +258,7 @@ static int pstore_decompress(void *in, void *out,
 
 static void allocate_buf_for_compression(void)
 {
-	if (!zbackend)
+	if (!IS_ENABLED(CONFIG_PSTORE_COMPRESS) || !zbackend)
 		return;
 
 	if (!crypto_has_comp(zbackend->name, 0, 0)) {
@@ -287,7 +287,7 @@ static void allocate_buf_for_compression(void)
 
 static void free_buf_for_compression(void)
 {
-	if (!IS_ERR_OR_NULL(tfm))
+	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && !IS_ERR_OR_NULL(tfm))
 		crypto_free_comp(tfm);
 	kfree(big_oops_buf);
 	big_oops_buf = NULL;