usb: gadget: u_audio: fix calculations for small bInterval

usb: gadget: u_audio: fix calculations for small bInterval

If bInterval is 1, then p_interval is 8000 and p_interval_mil is 8E9,
which is too big for a 32-bit value.  While the storage is indeed
64-bit, this value is used as the divisor in do_div() which will
truncate it into a uint32_t leading to incorrect calculated values.

Switch back to keeping the base value in struct snd_uac_chip which fits
easily into an int, meaning that the division can be done in two steps
with the divisor fitting safely into a uint32_t on both steps.

Fixes: 6fec018a7e70 ("usb: gadget: u_audio.c: Adding Playback Pitch ctl for sync playback")
Tested-by: Pavel Hofman <pavel.hofman@ivitera.com>
Signed-off-by: John Keeping <john@metanate.com>
Link: https://lore.kernel.org/r/20220104183243.718258-1-john@metanate.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>