x86/cc: Fix enum spelling to fix kernel-doc warnings

x86/cc: Fix enum spelling to fix kernel-doc warnings

Make the enum name in kernel-doc match the code to prevent kernel-doc warnings:

  Warning: include/linux/cc_platform.h:106 Enum value
   'CC_ATTR_GUEST_SEV_SNP' not described in enum 'cc_attr'
  Warning: include/linux/cc_platform.h:106 Excess enum value
   '%CC_ATTR_SEV_SNP' description in 'cc_attr'

Fixes: f742b90e61bb ("x86/mm: Extend cc_attr to include AMD SEV-SNP")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20251125022730.3163679-1-rdunlap@infradead.org