V4L/DVB (6743): cx25840: fix endianness inconsistency

cx25840_read4 reads a little-endian 32-bit value whereas cx25840_write4 writes
the 32-bit value as big-endian. Convert write4 to use little-endian as well
(that's the correct endianness).

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>