V4L/DVB (5441): Saa7146: Fix allocation of clipping memory

V4L/DVB (5441): Saa7146: Fix allocation of clipping memory

Olaf Hering pointed out that SAA7146_CLIPPING_MEM would become
very large for PAGE_SIZE > 4K.
In fact, the number of clipping windows is limited to 16,
and calculate_clipping_registers_rect() does not use more
than 256 bytes. SAA7146_CLIPPING_MEM adjusted accordingly.

Thanks-to: Olaf Hering <[email protected]>
Acked-by: Michael Hunold <[email protected]>
Signed-off-by: Oliver Endriss <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>