arm: zynq: Use unsigned type with comparison with ARRAY_SIZE

Sparse is return warning about this:
arch/arm/mach-zynq/slcr.c: In function 'zynq_slcr_get_mio_pin_status':
arch/arm/mach-zynq/slcr.c:185:16: warning: comparison between signed and
unsigned integer expressions [-Wsign-compare]
  for (i = 0; i < ARRAY_SIZE(mio_periphs); i++) {
                ^

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

arch/arm/mach-zynq/slcr.c

@@ -179,8 +179,9 @@ u32 zynq_slcr_get_idcode(void)
 int zynq_slcr_get_mio_pin_status(const char *periph)
 {
 	const struct zynq_slcr_mio_get_status *mio_ptr;
-	int val, i, j;
+	int val, j;
 	int mio = 0;
+	u32 i;
 
 	for (i = 0; i < ARRAY_SIZE(mio_periphs); i++) {
 		if (strcmp(periph, mio_periphs[i].peri_name) == 0) {