OMAP: HDMI: Don't release power constraints which were never added.

Make certain we don't call pm_qos_remove_request if we have never
added the request in the first place as it produces a nasty looking
error message and stack track in the kernel logs.

Change-Id: I1e955f15944908706f3a67cf6be0603478036ea5
Signed-off-by: John Grossman <johngro@google.com>
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@ti.com>