staging: cxt1e1: Add extern keyword for sparse 'static' warning

Resolve sparse "warning: symbol '...' was not declared.  Should it be static?"
messages.  Includes "comet_tables.h", which contains extern declarations for
the variables defined in comet_tables.c.

Signed-off-by: Shaun Laing <shaun@xresource.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>