[media] staging: easycap: Split easycap_delete() into several pieces

The patch splits easycap_delete(), which is in charge of
buffer deallocation, into smaller functions each
deallocating a specific kind of buffer.
Signed-off-by: Ezequiel Garcia <elezegarcia@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>