fix(rdn1edge): change variable type to fix gcc sign conversion error

Change variable type in function bl31_platform_setup() to fix the GCC
sign conversion error "comparison between signed and unsigned integer
expressions".

Signed-off-by: Tony K Nadackal <tony.nadackal@arm.com>
Change-Id: Iff914bd7ad521883723c8fb34dd893412cce7fc5
diff --git a/plat/arm/board/rdn1edge/rdn1edge_plat.c b/plat/arm/board/rdn1edge/rdn1edge_plat.c
index 1dbbf26..045c316 100644
--- a/plat/arm/board/rdn1edge/rdn1edge_plat.c
+++ b/plat/arm/board/rdn1edge/rdn1edge_plat.c
@@ -65,7 +65,8 @@
 #if defined(IMAGE_BL31)
 void bl31_platform_setup(void)
 {
-	int i, ret;
+	unsigned int i;
+	int ret;
 
 	if (plat_arm_sgi_get_multi_chip_mode() == 0 && CSS_SGI_CHIP_COUNT > 1) {
 		ERROR("Chip Count is set to %d but multi-chip mode not enabled\n",