arm64: zynqmp: Propagate error value from psu_init()

psu_init() returns int which wasn't declared and checked.
The patch is fixing function declarations and code to handle return
values properly.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

board/xilinx/zynqmp/zynqmp.c

@@ -237,15 +237,16 @@ static char *zynqmp_get_silicon_idcode_name(void)
 
 int board_early_init_f(void)
 {
+	int ret = 0;
 #if !defined(CONFIG_SPL_BUILD) && defined(CONFIG_CLK_ZYNQMP)
 	zynqmp_pmufw_version();
 #endif
 
 #if defined(CONFIG_SPL_BUILD) || defined(CONFIG_ZYNQMP_PSU_INIT_ENABLED)
-	psu_init();
+	ret = psu_init();
 #endif
 
-	return 0;
+	return ret;
 }
 
 #define ZYNQMP_VERSION_SIZE	9