Jabra Evolve 65 headset appears as if supporting lower rates than
48kHz, but it actually doesn't work but with 48kHz for playback.

This patch applies a workaround to enforce the 48kHz like LINE6
devices already did.  The workaround is put in a unified helper
function, set_fixed_rate(), to be called from both places now.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206149
Link: https://lore.kernel.org/r/20200211111419.5895-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>