ARM: dts: dra7: fix pinmux@1400 resource length

We need to add 4 bytes to include the last 32-bit register space.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>