[ARM] 4149/1: AT91: Overrun in SAM9 gettimeoffset().

Fix an overrun in the AT91SAM9 gettimeoffset() function.  This causes
the time value returned by gettimeofday() to jump "backwards".

Original patch from Michel Benoit.

Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>