staging: drm/omap: Add error handling

This patch adds fail checks for kmalloc and kzalloc calls
and also adds a error path that frees allocated pages by
introducing a call to _drm_gem_put_pages.

Signed-off-by: Emil Goode <emilgoode@gmail.com>
Signed-off-by: Rob Clark <rob@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>