arm64: zynqmp: avoid out of buffer access

strncat(a, b, c) appends a maximum of c characters plus the 0 byte
to a.

In board_init we first write 4 characters plus 0 byte to version.
So only ZYNQMP_VERSION_SIZE - 5 additional characters fit into
version.

The problem was indicated by cppcheck.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

board/xilinx/zynqmp/zynqmp.c

@@ -172,10 +172,10 @@ int board_init(void)
 	if (current_el() != 3) {
 		static char version[ZYNQMP_VERSION_SIZE];
 
-		strncat(version, "xczu", ZYNQMP_VERSION_SIZE);
+		strncat(version, "xczu", 4);
 		zynqmppl.name = strncat(version,
 					zynqmp_get_silicon_idcode_name(),
-					ZYNQMP_VERSION_SIZE);
+					ZYNQMP_VERSION_SIZE - 5);
 		printf("Chip ID:\t%s\n", zynqmppl.name);
 		fpga_init();
 		fpga_add(fpga_xilinx, &zynqmppl);