crypto: ccp - Fix checks for SNP_VLEK_LOAD input buffer length

The SNP_VLEK_LOAD IOCTL currently fails due to sev_cmd_buffer_len()
returning the default expected buffer length of 0 instead of the correct
value, which would be sizeof(struct sev_user_data_snp_vlek_load). Add
specific handling for SNP_VLEK_LOAD so the correct expected size is
returned.

Reported-by: Diego GonzalezVillalobos <Diego.GonzalezVillalobos@amd.com>
Cc: Diego GonzalezVillalobos <Diego.GonzalezVillalobos@amd.com>
Fixes: 332d2c1d ("crypto: ccp: Add the SNP_VLEK_LOAD command")
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>