sound: Move prototype declaration to header file oss/pas2.h from oss/pas2_card.c

Move prototype declaration of function to header file oss/pas2.h
from oss/pas2_card.c because it is used by more than one file.

This eliminates the following warnings in oss/pas2_mixer.c:
sound/oss/pas2_mixer.c:62:1: warning: no previous prototype for ‘mix_write’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>

sound/oss/pas2.h

···
 /*	From pas_midi.c */
 void pas_midi_init(void);
 void pas_midi_interrupt(void);
+
+/*	From pas2_mixer.c*/
+void mix_write(unsigned char data, int ioaddr);

sound/oss/pas2_card.c

···
  * to support other than the default base address
  */
 
-extern void     mix_write(unsigned char data, int ioaddr);
-
 unsigned char pas_read(int ioaddr)
 {
 	return inb(ioaddr + pas_translate_code);