By the time you hit that stage the driver is already loaded and DriverEntry has already been called. To step through DriverEntry you need to set a breakpoint with bu:
bu kmdfsmall!driverentry
And then disable/enable the device on the target. This will cause the driver to be reloaded and your breakpoint hit.
FYI your topic is misleading. The INF is the installation file used to install your driver image, the driver itself is the SYS file.