fw-api: fix a compilation error for HL target

If CONFIG_HIF_SDIO enabled, the extern reference
of function target_register_tbl_attach() in bmi_msg.h
conflict with its prototype defined in qca-wifi-host-cmn.

Delete the extern reference since it's useless here.

Change-Id: I441ab584758f6d61259dd70a6bdb151b6e2a72e4
CRs-Fixed: 2004353

fw/bmi_msg.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012 The Linux Foundation. All rights reserved.
+ * Copyright (c) 2012, 2017 The Linux Foundation. All rights reserved.
  *
  * Previously licensed under the ISC license by Qualcomm Atheros, Inc.
  *
@@ -263,8 +263,6 @@ PREPACK struct bmi_target_info {
 #define TARGET_TYPE_IPQ4019     16 /* dakota */
 #define TARGET_TYPE_QCA9888     17 /* besra */
 
-extern void target_register_tbl_attach(A_UINT32 target_type);
-
 #define BMI_ROMPATCH_INSTALL               9
         /*
          * Semantics: Install a ROM Patch.