[media] ddbridge: add i2c_read_regs()

Adds new i2c_read_regs() function and make i2c_read_reg() wrap into this
with len=1. Required for the tuner_tda18212_ping() and XO2 handling
functions (part of the Sony CXD28xx support patch series).

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>