Bluetooth: add printf format attribute to hci_set_[fh]w_info()

Commit 5177a838

 ("Bluetooth: Add debugfs fields for hardware and
firmware info") introduced hci_set_hw_info() and hci_set_fw_info().
These functions use kvasprintf_const() but are not marked with a
__printf attribute.  Adding such an attribute helps detecting issues
related to printf-formatting at build time.

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>