xtensa: Fix spelling/grammar in comment

Change 'excpetion' to 'exception', 'handeled' to 'handled' and 'the the'
to 'the'.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Message-Id: <20200525230413.15551-1-chris.packham@alliedtelesis.co.nz>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>