ehci: hsic: Disable hsic system clock during reset sequence

xcvr clock needs to be turned off before de-asserting clock
reset to hsic controller to prevent phy lock up. However, xcvr
clock is defined as parent of system clock, which is always on
during hsic controller reset, prevents xcvr clock being turned
off. Turn off system clock to turn off both system & xcvr clocks
during hsic controller clock reset. Also, simplify reset routine
by removing unnecessary code and delays.

Change-Id: Ic5fb667b4686a724d5ecfc034770f1e7db92b4d6
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>