Bug causing indefinite block on serial_close android

Mistakenly, I was trying to close the ftdi device after freeing its ftdi
context. This was causing an indefinite blockage on serial_close function call
at libusb_release_interface. Fixed it.

Signed-off-by: Venkatesh Shukla <venkatesh.shukla.eee11@iitbhu.ac.in>