ALSA: fix emu8000 DRAM sizing for AWE64 Value

Applicable to any kernel since 2013:

The special case added in commit 1338fc97 did not handle the possibility
that the address space on an AWE64 Value would wrap around at 512 KiB.  That
is what it does, so the memory is still not detected on those cards.

Fix that with a logic clean-up that eliminates the need for a special case.

Signed-off-by: David Flater <dave@flaterco.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>