io_block: define MAX_IO_BLOCK_DEVICES as unsigned

This is used as a table index, and already compared with an unsigned int:
block_dev_count.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/plat/socionext/uniphier/include/platform_def.h b/plat/socionext/uniphier/include/platform_def.h
index 3d71db2..6e9b98e 100644
--- a/plat/socionext/uniphier/include/platform_def.h
+++ b/plat/socionext/uniphier/include/platform_def.h
@@ -53,7 +53,7 @@
 
 #define MAX_IO_HANDLES			2
 #define MAX_IO_DEVICES			2
-#define MAX_IO_BLOCK_DEVICES		1
+#define MAX_IO_BLOCK_DEVICES		U(1)
 
 #define TSP_SEC_MEM_BASE		(BL32_BASE)
 #define TSP_SEC_MEM_SIZE		((BL32_LIMIT) - (BL32_BASE))