Function fec_enet_clk_enable() was disabling this line leaving the PHY

Function fec_enet_clk_enable() was disabling this line leaving the PHY
without a running clock. This makes the PHY lose its internal state
requiring a reset of the PHY to be reactivated.

This patch enables the clk_enet_out once at probe() so that it remains
enabled during all MDIO accesses.

References:	https://github.com/digi-embedded/linux/commit/fa3f9ab2d2650ba6b24f2ef62ddedbf971e56d07#diff-28c0935b4b5bf1738a0ee788d25a18ffR1952
		https://patchwork.ozlabs.org/patch/549391/

Signed-off-by: Josep Orga <jorga@somdevices.com>