Input: ad7877, ad7879 - remove depreciated IRQF_SAMPLE_RANDOM flag

This patch removes depreciated IRQF_SAMPLE_RANDOM flags from
ad7877 and ad7879 touchscreen drivers.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>