crypto: ccp - avoid uninitialized variable warning

The added support for version 5 CCPs introduced a false-positive
warning in the RSA implementation:

drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This changes the code in a way that should make it easier for
the compiler to track the state of the sb_count variable, and
avoid the warning.

Fixes: 6ba46c7d ("crypto: ccp - Fix base RSA function for version 5 CCPs")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Gary R Hook <gary.hook@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>