Fix style/indendation issues in sound_ahi.c.

[AliceLR]

• Replace 4 space indentation with hard tabs.
• Fix various instances of function { being on the wrong line.
• Refactor init() to use early return like most other places in libxmp and xmp-cli.
• Cast AHINAME to CONST_STRPTR to avoid pointer signedness warnings (bebbo amiga-gcc uses signed char by default, API defines this to unsigned char).
• Clear active on init (avoids potential issues if the driver ever gets initialized twice in one session).

Only compile-tested with bebbo amiga-gcc 6.5.0b, so marking as draft for now.

[sezero]

Tested under linux-hosted i386 AROS.

Inverted condition for tmp in while loop of play():

--- sound_ahi.c~
+++ sound_ahi.c
@@ -149,11 +149,10 @@ static void play(void *b, int len) {
 		len -= chunk;
 		in += chunk;
 
-		tmp = CheckIO((struct IORequest *) AHIReq[active ^ 1]);
-
 		AHIReq[active]->ahir_Std.io_Data = AHIBuf[active];
 		AHIReq[active]->ahir_Std.io_Length = chunk;
+		tmp = CheckIO((struct IORequest *) AHIReq[active ^ 1]);
-		AHIReq[active]->ahir_Link = tmp ? AHIReq[active ^ 1] : NULL;
+		AHIReq[active]->ahir_Link = tmp ? NULL : AHIReq[active ^ 1];
 		SendIO((struct IORequest *) AHIReq[active]);
 		active ^= 1;
 	}

[AliceLR]

Inverted condition for tmp in while loop of play():

Should be fixed now.

[sezero]

Should be fixed now.

Yes.

[AliceLR]

I'm fairly certain this is equivalent to the old code and should still work (or at least have the same bugs as the old code). I may try to get the old adtools amigaos-cross-toolchain working, but this code does compile with my local build of bebbo's toolchain.