sound: oss: rename local change_bits to avoid powerpc bitsops.h definition

This collides with powerpc exported functions from bitops.h.  Rename the
local copy in the oss soundblaster mixer and ad1848 driver.

Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>