usb: host: ehci-msm: Conditionally call ehci suspend/resume

This patch fixes a suspend/resume issue where the driver is blindly
calling ehci_suspend/resume functions when the ehci hasn't been setup.
This results in a crash during suspend/resume operations.

Signed-off-by: Andy Gross <andy.gross@linaro.org>
Tested-by: Pramod Gurav <pramod.gurav@linaro.org>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>