egl/android: Get gralloc module in dri2_initialize_android() (v2)

egl/android: Get gralloc module in dri2_initialize_android() (v2)

Currently droid_open_device() gets a reference to the gralloc module
only for its own use and does not store it anywhere. To make it possible
to call gralloc methods from code added in further patches, let's
refactor current code to get gralloc module in dri2_initialize_android()
and store it in dri2_dpy.

v2: fixes from Emil's review:
 a) remove duplicate initialization of 'err'.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>