drivers: espi: Clear virtual wire interrupt before calling handler

Clearing virtual wire interrupt after calling handler may cause next
interrupt miss if the same virtual wire changes due to action in handler.
As the interrupt source is read from register, it can be cleared before
calling handler to avoid next interrupt miss due to action/delay in the
callback handler.

Signed-off-by: Venkataramana Kotakonda <venkataramana.kotakonda@intel.com>