ARM: mxs/imx28: remove now unused clock lookup "fec.0"

Commit b2878fa4

 (ARM: mx28: update clock and device name for dual fec
support) added only the new lookups without removing the old one.

Cc: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>