tools/x86/kcpuid: Dump the correct CPUID function in error

The tool uses the 16 least significant bits of the CPUID leaf as an
index into its array of CPUID function field descriptions.

However, when that index is non-existent, it uses the same, truncated
index to report it, which is wrong:

$ kcpuid -l 0x80000034
  ERR: invalid input index (0x34)

Use the original index number in the error message.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230426094107.27348-1-bp@alien8.de