Returning -ENOSYS as a result of truncate() breaks ability to write to
semihosting host's filesystem, so change the return value to 0. This
shouldn't cause any problems since all of the funcionlaity of
truncate() should is already handled by 'open' (via O_TRUNC) and
'write' (will automatically grow the file size when writing)
automatically

Unfortunately this was missed in original commit that introduced
semihosting

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>