clk: s3c64xx: Hookup SPI clocks correctly

In the move to this clock driver the hookups for the SPI clocks were
dropped, which causes my system Cragganmore (s3c6410 based) to be unable
to locate any spibus clocks. This patch adds them back in.

When taking the clock from the epll clock (SCLK) the rates on the SPI
bus are incorrect, this needs further debugging but the hookup here
should be correct and the problem should be else where.

The USBCLK case has been dropped because this requires the USB PHY to be
enabled.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Tomasz Figa <t.figa@samsung.com>