xhci: hsic: Disable power event irq during suspend

Spurious power event event irq is observed during device power
off which may result in unclocked register access if it races
hsic runtime suspend. Avoid the unclocked access by disabling
the interrupt while executing suspend routine.

Change-Id: I82f6407a08dc08d87402b616c612ea045b4d180c
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>