Revert "serial: clps711x: Give a chance to perform useful tasks during wait loop"

This reverts commit 63e3ad32,
since this not works as expected and produce runtime error:

BUG: sleeping function called from invalid context at drivers/tty/serial/clps711x.c:379
in_atomic(): 0, irqs_disabled(): 128, pid: 287, name: mount

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>