scull_init: Change insmod arg to .ko

We need to a supply *.ko file as argument to `insmod`.
Also make other minor shell script syntax correntions.

Signed-off-by: Salym Senyonga <salymsash@gmail.com>
main: minor code fixes

Minor code fixes for the DEBUG=y path.

Signed-off-by: Salym Senyonga <salymsash@gmail.com>