drivers: Fix typo in parameter description for driver_find_device_by_acpi_dev

Fix a typo in the comment describing the parameters for the new API, which
triggers the following warning for htmldocs:

include/linux/device.h:479: warning: Function parameter or member 'drv' not described in 'driver_find_device_by_acpi_dev'

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20190801102026.27312-2-suzuki.poulose@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>