ALSA: hda: check make_exec_verb() return value

If given a -1 cmd parameter then make_exec_verb() returns -1 without
setting the res output value.

Prior to this change snd_hda_codec_read() assumed that make_exec_verb()
unconditionally set res regardless of the cmd value.

This change explicitly checks the make_exec_verb() return value before
consuming the potentially unset res value.

Signed-off-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>