msm: pp2s: Remove unnecessary call to enable_irq()

request_irq() enables an interrupt source. Subsequent enable_irq()
call causes a warning, and can be removed safely.

Change-Id: Ia4a1667fe87ef4e2c0353831932be7f105d6be1f
Acked-by: Ho Lee <holee@qti.qualcomm.com>
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>