xilinx: zynqmp: Add the missing function prototype

Add missing prototype to fix the below sparse warning
warning: no previous prototype for 'spl_spi_get_uboot_offs'
	 [-Wmissing-prototypes]

Fixes: 2c8a09219cdb ("arm64: zynqmp: Add multiboot support for SPL/SPI offset calculation")
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20240207083328.1673752-1-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>
diff --git a/board/xilinx/zynqmp/zynqmp.c b/board/xilinx/zynqmp/zynqmp.c
index 9f50090..ba49eb7 100644
--- a/board/xilinx/zynqmp/zynqmp.c
+++ b/board/xilinx/zynqmp/zynqmp.c
@@ -18,6 +18,7 @@
 #include <ahci.h>
 #include <scsi.h>
 #include <soc.h>
+#include <spl.h>
 #include <malloc.h>
 #include <memalign.h>
 #include <wdt.h>