Input: ads7846 - use msleep() instead of udelay() in suspend

Sometimes a polling loop had a hard time changing state without
pre-emption enabled.  Use msleep instead, it's better anyway.

Signed-off-by: Juha Yrjola <juha.yrjola@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>