Coccinelle: Make 'report' the default mode

It appears that the 'report' mode is the one always
provided by the semantic patches included in the kernel.
It is thus more natural to select it by default.

The 'chain' mode is however kept and the 'patch' mode
is still the first tried in that case.

Signed-off-by: Nicolas Palix <nicolas.palix@imag.fr>
Signed-off-by: Michal Marek <mmarek@suse.cz>