Introduce clear_psp_master_device() to ensure that sp_dev_master gets
properly cleared on the release of a psp device.

Fixes: 2a6170df ("crypto: ccp: Add Platform Security Processor (PSP) device support")
Signed-off-by: John Allen <john.allen@amd.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>