m68knommu: define a local devm_clk_get() function

Commit f4d40de3 ("net fec: do not depend
on grouped clocks") breaks compilation of the FEC driver for non iMX
platforms in linux-3.5-rc1. For example when compiling for ColdFire I get:

      LD      vmlinux
    drivers/built-in.o: In function `fec_probe':
    fec.c:(.devinit.text+0x1e0): undefined reference to `devm_clk_get'

Define a simple devm_clk_get() function for the m68knommu architecture.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>