ALSA: emux: improve patch ioctl data validation

In load_data(), make the validation of and skipping over the main info
block match that in load_guspatch().

In load_guspatch(), add checking that the specified patch length matches
the actually supplied data, like load_data() already did.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Message-ID: <20240406064830.1029573-8-oswald.buddenhagen@gmx.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>