[PATCH] I2C: documentation update 1/3

This patch just changes the extension of Documentation/i2c/chips/smsc47b397.txt
to none - to conform with naming in i2c subsystem directory.

Signed-off-by: Rudolf Marek <r.marek@sh.cvut.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>