ARM: i.MX25: clk: parent per5_clk to AHB clock

ARM: i.MX25: clk: parent per5_clk to AHB clock

The mxc-timer on the imx25 needs to be derived from the AHB clock.
If a bootloader reparents this clock to the ipg_clk_highfreq, which according
to the datasheet is a valid operation, the system can/will produce lockups/
freezes after some time [1].

This can be forced with code like
	while(1)
                syscall(SYS_clock_gettime, CLOCK_REALTIME, &tp);

This was already fixed with the commit
	"i.MX25 GPT clock fix: ensure correct the clock source" [2],
for 3.1-rc2, but was lost, when i.MX was converted to the common clock framework
("ARM i.MX25: implement clocks using common clock framework") [3]

[1]: http://lists.arm.linux.org.uk/lurker/message/20130129.161230.229bda17.en.html
[2]: 2012d9ca2a1381ae3e733330a7f0d1d2f1988bba
[3]: 6bbaec5676e4f475b0d78743cbd4c70a8804ce14

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Cc: stable@vger.kernel.org # v3.5+
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>