ARM: dts: gta04: fix polarity of clocks for mcbsp4

The clock polarity setting of the mcbsp connected to
the modem was wrong so almost only noise
was received.
With this patch it is also the same as it was on
earlier non-dt kernels where it was working properly

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Signed-off-by: Tony Lindgren <tony@atomide.com>