remove minor_num from tty_driver

for kernels >= 3.4.0

it doesnt look like its beeing used anyways, so just get rid of it.

read:
commit 87cab16beb882d3f9e61a2c0184fa7cf76de1f90
use poll_requested_events(wait) instead of wait->key

for kernels >= 3.4.0

read:
commit 626cf236608505d376e4799adb4f7eb00a8594af
replace poll_table->key with poll_table->_key

for kernels >= 3.4.0

poll.h asks for not touching poll_table internals but we already
are doing nasty things with do_pollfd. so why not?

read:
commit 626cf236608505d376e4799adb4f7eb00a8594af
updated README - now were at linux-3.4.42