imx: mx7: fix potential overflow in imx_ddr_size()

The imx_ddr_size() function may overflow as it is possible to kind of
over provision the DDR controller. Fix this by capping it to 2 GB which
is the maximum allowed size as per reference manual.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/arch/arm/mach-imx/mx7/ddr.c b/arch/arm/mach-imx/mx7/ddr.c
index f19aeb8..9713835 100644
--- a/arch/arm/mach-imx/mx7/ddr.c
+++ b/arch/arm/mach-imx/mx7/ddr.c
@@ -196,5 +196,9 @@
 	if (field_val <= 29)
 		bits++;
 
+	/* cap to max 2 GB */
+	if (bits > 31)
+		bits = 31;
+
 	return 1 << bits;
 }