dev: gcdb: Fix compilation warnings

Add function declaration to appropriate header file to avoid
compilation warnings. It is done in an effort to enable WERROR.

Change-Id: Ifa611d2535a2f764e5b4b5adaecce30ca83d3beb
diff --git a/target/msm8994/oem_panel.c b/target/msm8994/oem_panel.c
index ac227a4..fca02c9 100644
--- a/target/msm8994/oem_panel.c
+++ b/target/msm8994/oem_panel.c
@@ -350,7 +350,7 @@
 	return pan_type;
 }
 
-bool oem_panel_select(const char *panel_name, struct panel_struct *panelstruct,
+int oem_panel_select(const char *panel_name, struct panel_struct *panelstruct,
 			struct msm_panel_info *pinfo,
 			struct mdss_dsi_phy_ctrl *phy_db)
 {