tmc-etr: Set drvdata mode as CS_MODE_SYSFS when enable usb mode

When enable usb mode, the drvdata mode should be CS_MODE_SYSFS and
the refcnt need to be increased.

Change-Id: I82f04846bde4c4e442e37fde09a3e08872df26d0
Signed-off-by: Mao Jinlong <jinlmao@codeaurora.org>