ALSA: doc: Fix PCM interface section typos

Fix two mistakes in the PCM interface section:
1/ Members of the snd_pcm_hardware structure are channels_{min,max}
   and not channel_{min,max} (mind the 's').
2/ Another sentence is incomplete as the reference to one structure
   member (period_bytes_max) is missing.

There is no relevant 'Fixes:' tag to apply as both typos predate the
Git era.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20230130162924.119389-1-miquel.raynal@bootlin.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/kernel-api/writing-an-alsa-driver.rst

@@ -1720,16 +1720,16 @@ Typically, you'll have a hardware descriptor as below:
 -  ``rate_min`` and ``rate_max`` define the minimum and maximum sample
    rate. This should correspond somehow to ``rates`` bits.
 
--  ``channel_min`` and ``channel_max`` define, as you might already
+-  ``channels_min`` and ``channels_max`` define, as you might already
    expected, the minimum and maximum number of channels.
 
 -  ``buffer_bytes_max`` defines the maximum buffer size in
    bytes. There is no ``buffer_bytes_min`` field, since it can be
    calculated from the minimum period size and the minimum number of
-   periods. Meanwhile, ``period_bytes_min`` and define the minimum and
-   maximum size of the period in bytes. ``periods_max`` and
-   ``periods_min`` define the maximum and minimum number of periods in
-   the buffer.
+   periods. Meanwhile, ``period_bytes_min`` and ``period_bytes_max``
+   define the minimum and maximum size of the period in bytes.
+   ``periods_max`` and ``periods_min`` define the maximum and minimum
+   number of periods in the buffer.
 
    The “period” is a term that corresponds to a fragment in the OSS
    world. The period defines the size at which a PCM interrupt is