ALSA: scarlett2: Fix redeclaration of loop variable

Was using both "for (i = 0, ..." and "for (int i = 0, ..." in
scarlett2_update_autogain(). Remove "int" to fix.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/ecb0a8931c1883abd6c0e335c63961653bef85f0.1727971672.git.g@b4.vu