drivers: nordic_nrf_temp: nrfx: Fix build warning into temp_nrf5_init

Building lwm2m_client with CONFIG_NET_L2_OPENTHREAD=y leads to
following warning during build:

west build -s samples/net/lwm2m_client -b nrf52840dk_nrf52840 -- \
				-DCONFIG_NET_L2_OPENTHREAD=y

zephyr/drivers/sensor/nrf5/temp_nrf5.c:115:10:
warning: zero-length gnu_printf format string [-Wformat-zero-length]
115 |  LOG_DBG("");

Signed-off-by: Kiril Petrov <retfie@gmail.com>