V4L/DVB (4784): [saa7146_i2c] short_delay mode fixed for fast machines

TT DVB-C 2300 runs at 137 kHz I2C speed. short_delay mode did not work
reliably on fast machines with that speed. Increased max loop count from
20 to 50. Moved dummy access out of the loop.

Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>