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>

arch/arm/mach-imx/mx7/ddr.c

@@ -196,5 +196,9 @@ unsigned int imx_ddr_size(void)
 	if (field_val <= 29)
 		bits++;
 
+	/* cap to max 2 GB */
+	if (bits > 31)
+		bits = 31;
+
 	return 1 << bits;
 }