staging: kpc2000: rename variables with kpc namespace

Some namings in kpc2000_i2c are too ambiguous that may causing
confusion to the readers.

Rename some variable, function and struct name to prefix with 'kpc_i2c'
to eliminate confusions.

Signed-off-by: Jerry Lin <wahahab11@gmail.com>
Link: https://lore.kernel.org/r/20200121024620.GA10842@compute1


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>