drivers: charger: fix i2c_dump_msgs_rw argument

Fixes:

zephyr/drivers/charger/emul_sbs_charger.c:70:26: warning: passing
argument 1 of ‘i2c_dump_msgs_rw’ from incompatible pointer type
[-Wincompatible-pointer-types]

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>