xtensa: fix change_bit in exclusive access option

change_bit implementation for XCHAL_HAVE_EXCLUSIVE case changes all bits
except the one required due to copy-paste error from clear_bit.

Cc: stable@vger.kernel.org # v5.2+
Fixes: f7c34874 ("xtensa: add exclusive atomics support")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>