V4L/DVB (7750): au0828/ cleanups and fixes

This patch contains the following cleanups and fixes:
- "debug" is definitely not a good name for a global variable,
  renamed it to "au0828_debug"
  this fixes a compile error with some kernel configurations
- since the module parameter is int the variable shouldn't be unsigned
- remove the {usb,bridge,i2c}_debug module parameters since they are
  already covered by the "debug" module parameter
- remove the unused au0828_bcount
- make the needlessly global i2c_scan static
- make the needlessly global dvb_register() static

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>