xfrm: fix boolean assignment in xfrm_get_type_offload

Assign true or false to boolean variables instead of an integer value.

This issue was detected with the help of Coccinelle.

Fixes: ffdb5211

 ("xfrm: Auto-load xfrm offload modules")
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>