x86/ucode: Fold early_update_cache() into its single caller

x86/ucode: Fold early_update_cache() into its single caller

The data pointer is known good, so the -ENOMEM path is unnecessary.  However,
if we find no patch, something's wrong seeing as early_microcode_init()
indicated it was happy.

We are the entity initialising the cache, so we don't need the complexity of
using microcode_update_cache().  Just assert the cache is empty, and populate
it.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>