lme2510_state exists for the entire duration of driver.

Move usb_buffer to lme2510_state removing the need for
lme2510_exit_int for removing the buffer.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>