msm: pcie: correct clock frequency allocation

When getting the size for PCIe clock frequencies
table from devicetree, use clock frequency entry
instead of clock names since these two are
not one-to-one.

Change-Id: I30fb2718c2adb2abd9536d19f439ca750b7fb1c3
Signed-off-by: Tony Truong <truong@codeaurora.org>