sound: fix OSS MIDI output data loss

In the 2.1.6 kernel, the output loop in midi_poll() was changed to
enable interrupts during the outputc() call.  Unfortunately, the check
whether the device has accepted the current byte ("ok") was moved behind
the code that removes the byte from the output queue, so one byte would
be lost every time the hardware FIFO is full.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>