AVR32: fix timer_init() function

AVR32: fix timer_init() function

timer_init() now returns an int (the error code) instead of void.
This makes compilation fail with:

interrupts.c:111: error: conflicting types for 'timer_init'
/home/svens/u-boot/u-boot/include/common.h:246: error: previous
declaration of 'timer_init' was here
make[1]: *** [interrupts.o] Error 1

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Acked-by: Andreas Bießmann <andreas.devel@googlemail.com>
Signed-off-by: Anatolij Gustschin <agust@denx.de>