drm/amd/display: Fix kernel panic by dal_gpio_open() error

Currently both error code paths handled in dal_gpio_open_ex() issues
ASSERT_CRITICAL(), and this leads to a kernel panic unnecessarily if
CONFIG_KGDB is enabled.  Since basically both are non-critical errors
and can be recovered, drop those assert calls and use a safer one,
BREAK_TO_DEBUGGER(), for allowing the debugging, instead.

BugLink: https://bugzilla.opensuse.org/show_bug.cgi?id=1177973


Cc: <stable@vger.kernel.org>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>