i2c: at91: fixup return type of wait_for_completion_timeout

Return type of wait_for_completion_timeout is unsigned long not int. This
patch adds a timeout variable of appropriate type and fixes up the assignment.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>