V4L/DVB (13537): ir: Prepare the code for dynamic keycode table allocation

Currently, the IR table is initialized by calling ir_input_init(). However,
this function doesn't return any error code, nor has a function to be called
when de-initializing the IR's.

Change the return argment to integer and make sure that each driver will
handle the error code. Also adds a function to free any resources that may
be allocating there: ir_input_free().

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>