ALSA: sbawe: fix memory detection

Memory amount is increased before a successful write-read
sequence is done. Thus, 512 kB of onboard memory is detected
on memoryless cards like SB32.

Move the increasing of memory counter after successful read
is done.

Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>