lib: Use correct type for return value

The error check 'plic_off < 0' does nothing, since plic_off is stored as
a u32. Fix this by changing it to an int, which matches the return type of
fdt_node_offset_by_compatible().

Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

lib/utils/irqchip/plic.c

@@ -51,7 +51,7 @@ void plic_fdt_fixup(void *fdt, const char *compat)
 {
 	u32 *cells;
 	int i, cells_count;
-	u32 plic_off;
+	int plic_off;
 
 	plic_off = fdt_node_offset_by_compatible(fdt, 0, compat);
 	if (plic_off < 0)