drm/omap: omap_irq: Fix a couple of doc-rot issues

The API has been updated, but the header was not.

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/omapdrm/omap_irq.c:115: warning: Function parameter or member 'crtc' not described in 'omap_irq_enable_vblank'
 drivers/gpu/drm/omapdrm/omap_irq.c:115: warning: Excess function parameter 'dev' description in 'omap_irq_enable_vblank'
 drivers/gpu/drm/omapdrm/omap_irq.c:115: warning: Excess function parameter 'pipe' description in 'omap_irq_enable_vblank'
 drivers/gpu/drm/omapdrm/omap_irq.c:142: warning: Function parameter or member 'crtc' not described in 'omap_irq_disable_vblank'
 drivers/gpu/drm/omapdrm/omap_irq.c:142: warning: Excess function parameter 'dev' description in 'omap_irq_disable_vblank'
 drivers/gpu/drm/omapdrm/omap_irq.c:142: warning: Excess function parameter 'pipe' description in 'omap_irq_disable_vblank'

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Rob Clark <rob.clark@linaro.org>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201105144517.1826692-5-lee.jones@linaro.org