scripts/tags.sh: Fix warnings "null expansion of name pattern"

Warnings such as
ctags: Warning: include/linux/wait_bit.h:59: null expansion of name pattern "\1"
are triggered when parsing DECLARE_BITMAP() inside comments,
resulting in an empty token.

To avoid this, ensure only non-empty tokens.

Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Link: https://lore.kernel.org/r/20241025130322.3077455-1-costa.shul@redhat.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>