CLK: TI: OMAP4/5/DRA7: Remove gpmc_fck from dummy clocks

When arch/arm/mach-omap2/gpmc.c calls clk_get(..., "fck"), it will
get a dummy clock and try to use it. As the rate is configured to zero,
this will result in several divisions by zero, and misconfigured
timings, with devices on the bus being lost in the La La Land.

It is better to remove gpmc_fck from the dummy clocks, so that gpmc.c
can fail gracefully.

Cc: stable@vger.kernel.org # v3.14+
Signed-off-by: Florian Vaussard <florian.vaussard@epfl.ch>
Acked-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>