ALSA: usb-audio: Optimize the copy of packet sizes for implicit fb handling

ALSA: usb-audio: Optimize the copy of packet sizes for implicit fb handling

We did manual copies over loop for the packet data update of the
implicit feedback, but this can be optimized with a simple memcpy().

Along with it, change the data type of snd_usb_packet_info struct to
align with other (from uint32_t to int).

No functional changes but only code optimizations.

Link: https://patch.msgid.link/20260216141209.1849200-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>