[pax] ALSA: seq_oss: fix prototype of readq_dump_sysex()

The second argument should be a const pointer under PaX/grsec.

This fixes the following build breakage:

 sound/core/seq/oss/seq_oss_readq.c: In function ‘snd_seq_oss_readq_sysex’:
 sound/core/seq/oss/seq_oss_readq.c:146:36: error: passing argument 2 of ‘snd_seq_dump_var_event’ from incompatible pointer type [-Werror=incompatible-pointer-types]
   return snd_seq_dump_var_event(ev, readq_dump_sysex, &ctx);

Reported-by: sempervictus in #14
Reported-by: powerman in #15
Signed-off-by: Mathias Krause <minipli@googlemail.com>

sound/core/seq/oss/seq_oss_readq.c

@@ -126,7 +126,7 @@ struct readq_sysex_ctx {
 	int dev;
 };
 
-static int readq_dump_sysex(void *ptr, void *buf, int count)
+static int readq_dump_sysex(void *ptr, const void *buf, int count)
 {
 	struct readq_sysex_ctx *ctx = ptr;