lib/Kconfig: Correct typo about SYSINFO_SMBIOS in help message

The correct symbol to enable to have SMBIOS populate fields based on the
device tree is SYSINFO_SMBIOS and not SMBIOS_SYSINFO.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>