media: rcar-dma: p_set can't be NULL

The only way for p_set to be NULL would be if vin_coef_set would be an
empty array.

On such case, the driver will OOPS, as it would try to de-reference a
NULL value. So, the check if p_set is not NULL doesn't make any sense.

Solves those two smatch warnings:

	drivers/media/platform/rcar-vin/rcar-dma.c:489 rvin_set_coeff() warn: variable dereferenced before check 'p_set' (see line 484)
	drivers/media/platform/rcar-vin/rcar-dma.c:494 rvin_set_coeff() error: we previously assumed 'p_set' could be null (see line 489)

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>