crypto: aspeed - fix uninitialized symbol 'idx' warning

'idx' is not initialized if it's not EXP_MODE nor MOD_MODE.
Use "else" instead to fix it.
Signed-off-by: Neal Liu <neal_liu@aspeedtech.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/202302261052.CVFRyq6F-lkp@intel.com/Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/aspeed/aspeed-acry.c

@@ -289,7 +289,7 @@ static int aspeed_acry_rsa_ctx_copy(struct aspeed_acry_dev *acry_dev, void *buf,
 
 			if (mode == ASPEED_RSA_EXP_MODE)
 				idx = acry_dev->exp_dw_mapping[j - 1];
-			else if (mode == ASPEED_RSA_MOD_MODE)
+			else /* mode == ASPEED_RSA_MOD_MODE */
 				idx = acry_dev->mod_dw_mapping[j - 1];
 
 			dw_buf[idx] = cpu_to_le32(data);