media: atomisp: Simplify atomisp_s_input() input argument checking

Simplify the checking of the input argument to atomisp_s_input():
- Remove the check for input >= ATOM_ISP_MAX_INPUTS, input_cnt
  never is > ATOM_ISP_MAX_INPUTS so checking only that is sufficient
- Remove the unnecessary camera local variable
- Move the 2 invalid argument checks to above the atomisp_pipe_check()
  which checks if the pipe is busy or not

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>