media: rcar-vin: work around -Wenum-compare-conditional warning

clang-19 warns about mixing two enum types here:

drivers/media/platform/renesas/rcar-vin/rcar-vin.h:296:12: error: conditional expression between different enumeration types ('enum rvin_csi_id' and 'enum rvin_isp_id') [-Werror,-Wenum-compare-conditional]
drivers/media/platform/renesas/rcar-vin/rcar-core.c:216:18: error: conditional expression between different enumeration types ('enum rvin_csi_id' and 'enum rvin_isp_id') [-Werror,-Wenum-compare-conditional]
drivers/media/platform/renesas/rcar-vin/rcar-vin.h:296:12: error: conditional expression between different enumeration types ('enum rvin_csi_id' and 'enum rvin_isp_id') [-Werror,-Wenum-compare-conditional]
drivers/media/platform/renesas/rcar-vin/rcar-vin.h:296:12: error: conditional expression between different enumeration types ('enum rvin_csi_id' and 'enum rvin_isp_id') [-Werror,-Wenum-compare-conditional]

This one is intentional, and there is already a cast to work around another
warning, so address this by adding another cast.

Fixes: 406bb586 ("media: rcar-vin: Add r8a779a0 support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>