hamradio: drop ISA_DMA_API dependency

It looks like the dependency got added accidentally in commit a5532606


("[PATCH] ISA DMA Kconfig fixes - part 3"). Unlike the previously removed
dmascc driver, the scc driver never used DMA.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>