ALSA: hda/ca0132 - Simplify alt firmware loading code

ca0132 codec driver loads the firmware selectively depending on the
model in addition to the fallback of the default firmware.  The code
works good, but a minor problem is that the current code seems
confusing for Clang where it spews a warning about uninitialized
variable.

This patch simplifies the code flow for such a false-positive
warning.  After this refactoring, the ca0132_spec.alt_firmware_present
field is no longer used, hence it's eliminated as well.

Reported-and-tested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>