change size arg type in kmem_cache_create

change the size argument's type, in kmem_cache_create to size_t
from int.

Also correct the successful mem allocation condition to check for
false before returning -ENOMEM. This was likely causing insmod to
choke with "Can't allocate memory"

Signed-off-by: Salym Senyonga <salymsash@gmail.com>
main.c: create `/sys` and hence `/dev` entries

Provide mechanism to automatically create /dev entries.

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