host_event_commands: Fix lpc_get_next_host_event for 64-bit events
host_event_commands: Fix lpc_get_next_host_event for 64-bit events

__builtin_ffs takes an int as argument, and, therefore, does not
find bits >= 32. Fix this up when CONFIG_HOST_EVENT64.

BUG=b:69329196
BRANCH=fizz,poppy
TEST=Patch coreboot to add bit 33 in SCI mask, add EC code to send
     such events, EC does not watchdog anymore

Change-Id: If868095f19fe1940b4f5924cf669a719f9535991
Signed-off-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/989514
Reviewed-by: Furquan Shaikh <6be5c96c464778f89679b1062a2e0a6af93d2aa5@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec