drivers/usb/hub/acpi.c: Don't use heap for ACPI name

Using malloc would increase the heap use each time this function is
called. Instead allocate a per struct device buffer inside the
chip_info struct.

Found by coverity scan, CID 1488815.

Change-Id: Ie24870b34338624b3bf3a6f420debdd24a68ffbd
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64338
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
diff --git a/src/drivers/usb/hub/acpi.c b/src/drivers/usb/hub/acpi.c
index 347e25e..10e38fb6 100644
--- a/src/drivers/usb/hub/acpi.c
+++ b/src/drivers/usb/hub/acpi.c
@@ -8,8 +8,11 @@
 
 static const char *usb_hub_acpi_name(const struct device *dev)
 {
-	char *name;
 	const char *pattern;
+	struct drivers_usb_hub_config *config = dev->chip_info;
+
+	if (config->acpi_name[0] != 0)
+		return config->acpi_name;
 
 	/* USB ACPI driver does not have acpi_name operation defined. Hence return
 	   the ACPI name for both the hub and any downstream facing ports. */
@@ -26,11 +29,10 @@
 		return NULL;
 	}
 
-	name = malloc(ACPI_NAME_BUFFER_SIZE);
-	snprintf(name, ACPI_NAME_BUFFER_SIZE, pattern, dev->path.usb.port_id + 1);
-	name[4] = '\0';
+	snprintf(config->acpi_name, sizeof(config->acpi_name), pattern,
+		 dev->path.usb.port_id + 1);
 
-	return name;
+	return config->acpi_name;
 }
 
 static void usb_hub_add_ports(const struct device *dev)