fbdev: da8xx-fb: go to proper label on error handling paths in probe

fb_probe() can successfully allocate a new frame buffer, but then fail
to perform some operations with regulator. In these cases fb_probe()
goes to label err_pm_runtime_disable where the frame buffer is not
released. The patch makes fb_probe() to go to label err_release_fb on
corresponding error handling paths.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Evgeny Novikov <novikov@ispras.ru>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200702160540.24546-1-novikov@ispras.ru