cxl/test: Simplify fw_buf_checksum_show()

First, just use sha256() instead of a sequence of sha256_init(),
sha256_update(), and sha256_final(). The result is the same.

Second, use *phN instead of open-coding the conversion of bytes to hex.

Acked-by: Ard Biesheuvel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Eric Biggers <[e-mail]>

tools/testing/cxl/test/mem.c

···
 {
 	struct cxl_mockmem_data *mdata = dev_get_drvdata(dev);
 	u8 hash[SHA256_DIGEST_SIZE];
-	unsigned char *hstr, *hptr;
-	struct sha256_state sctx;
-	ssize_t written = 0;
-	int i;
 
-	sha256_init(&sctx);
-	sha256_update(&sctx, mdata->fw, mdata->fw_size);
-	sha256_final(&sctx, hash);
+	sha256(mdata->fw, mdata->fw_size, hash);
 
-	hstr = kzalloc((SHA256_DIGEST_SIZE * 2) + 1, GFP_KERNEL);
-	if (!hstr)
-		return -ENOMEM;
-
-	hptr = hstr;
-	for (i = 0; i < SHA256_DIGEST_SIZE; i++)
-		hptr += sprintf(hptr, "%02x", hash[i]);
-
-	written = sysfs_emit(buf, "%s\n", hstr);
-
-	kfree(hstr);
-	return written;
+	return sysfs_emit(buf, "%*phN\n", SHA256_DIGEST_SIZE, hash);
 }
 
 static DEVICE_ATTR_RO(fw_buf_checksum);