ARM: bcm2835: follow dt uart node-naming convention

This patch fixes the naming of the device tree node: uart@7e201000
to conform to the standard of: serial@7e201000

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
[anholt: Rebased on 2835.dtsi -> 283x.dtsi change]
Signed-off-by: Eric Anholt <eric@anholt.net>