usb: musb: core: remove unnecessary reg access from resume IRQ

when musb is operating as host and a remote wakeup
fires up, a resume interrupt will be raised. At that
point SUSPENDM bit is automatically cleared and
RESUME bit is automatically set.

Remove those two from IRQ handler.

Tested-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>