sound: Kconfig: drop unknown symbol ARCH_CLPS7500

Commit 635f0258 ("[ARM] clps7500: remove support") missed one instance
of the ARCH_CLPS7500 Kconfig symbol. Drop it now.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>