[media] media: s5p-mfc: fix mmap support for 64bit arch

TASK_SIZE is depends on the systems architecture (32 or 64 bits) and it
should not be used for defining offset boundary for mmaping buffers for
CAPTURE and OUTPUT queues. This patch fixes support for MMAP calls on
the CAPTURE queue on 64bit architectures (like ARM64).

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>