ALSA: Fix a const to non-const assignment in the Digigram VXpocket sound driver

Fix a const to non-const pointer assignment warning in the Digigram VXpocket
sound driver.

This may be due to patch 0aa4937648b91e9e6d3879b2cbeaa5f0c9863ac0.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

sound/pcmcia/vx/vxp_ops.c

@@ -151,7 +151,7 @@ static int vxp_load_xilinx_binary(struct vx_core *_chip, const struct firmware *
 	unsigned int i;
 	int c;
 	int regCSUER, regRUER;
-	unsigned char *image;
+	const unsigned char *image;
 	unsigned char data;
 
 	/* Switch to programmation mode */