crypto: caam - Avoid GCC memset bug warning

Certain versions of gcc don't like the memcpy with a NULL dst
(which only happens with a zero length).  This only happens
when debugging is enabled so add an if clause to work around
these warnings.

A similar warning used to be generated by sparse but that was
fixed years ago.

Link: https://lore.kernel.org/lkml/[email protected]
Reported-by: kernel test robot <[email protected]>
Reported-by: Kees Cook <[email protected]>
Reported-by: Uwe Kleine-König <[email protected]>
Tested-by: Uwe Kleine-König <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

Author: herbertx

drivers/crypto/caam/desc_constr.h

@@ -163,7 +163,8 @@ static inline void append_data(u32 * const desc, const void *data, int len)
 {
 	u32 *offset = desc_end(desc);
 
-	if (len) /* avoid sparse warning: memcpy with byte count of 0 */
+	/* Avoid gcc warning: memcpy with data == NULL */
+	if (!IS_ENABLED(CONFIG_CRYPTO_DEV_FSL_CAAM_DEBUG) || data)
 		memcpy(offset, data, len);
 
 	(*desc) = cpu_to_caam32(caam32_to_cpu(*desc) +