ALSA: scarlett2: Allow passing any output to line_out_remap()

ALSA: scarlett2: Allow passing any output to line_out_remap()

Line outputs 3 & 4 on the Gen 3 18i8 are internally the analogue 7 and
8 outputs, and this renumbering is hidden from the user by
line_out_remap(). By allowing higher values (representing non-analogue
outputs) to be passed to line_out_remap(), repeated code from
scarlett2_mux_src_enum_ctl_get() and scarlett2_mux_src_enum_ctl_put()
can be removed.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/3b70267931f5994628ab27306c73cddd17b93c8f.1698342632.git.g@b4.vu
Signed-off-by: Takashi Iwai <tiwai@suse.de>