crypto: nx - Fix uninitialised hv_nxc on error

The compiler correctly warns that hv_nxc may be used uninitialised
as that will occur when NX-GZIP is unavailable.

Fix it by rearranging the code and delay setting caps_feat until
the final query succeeds.

Fixes: b4ba2211 ("crypto/nx: Get NX capabilities for GZIP coprocessor type")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>