Ensure functions return a value

otherwise, gcc errored out
because non-void functions are supposed to return a value.

Alternatively, we could change the declaration to `void`.

scsiapi/scsiapi_linux.c

@@ -218,6 +218,7 @@ int scsi_write(struct scsi_device * dev, const unsigned char * data, size_t data
     | Send pass through command                             |
     \*-----------------------------------------------------*/
     ioctl(dev->fd, SG_IO, &header);
+    return 0;
 }
 
 #ifdef __cplusplus

scsiapi/scsiapi_macos.c

@@ -60,7 +60,7 @@ struct scsi_device * scsi_open_path(const char *path)
 
 int scsi_write(struct scsi_device * dev, const unsigned char * data, size_t data_length, const unsigned char * cdb, size_t cdb_length, unsigned char * sense, size_t sense_length)
 {
-
+    return 0;
 }
 
 #ifdef __cplusplus

scsiapi/scsiapi_windows.c

@@ -235,6 +235,7 @@ int scsi_write(struct scsi_device * dev, const unsigned char * data, size_t data
     | Free the buffer                                       |
     \*-----------------------------------------------------*/
     free(buffer);
+    return 0;
 }
 #ifdef __cplusplus
 }