egl/android: Respect buffer mask in droid_image_get_buffers (v2)

egl/android: Respect buffer mask in droid_image_get_buffers (v2)

Drivers can request different set of buffers depending on the buffer
mask they pass to the get_buffers callback. This patch makes
droid_image_get_buffers() respect this mask.

v2: Return error only in case of real error condition and ignore requests
    of unavailable buffers.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Tested-by: Rob Herring <rob@kernel.org>
Reviewed-by: Chad Versace <chad@kiwitree.net>
Change-Id: I6c3c4eca90f4c618579f6725dec323c004cb44ba