audio: fix buffer-length typo in documentation

Fixes: f0b3d811529 ("audio: -audiodev command line option: documentation")
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190918095335.7646-2-stefanha@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/qemu-options.hx b/qemu-options.hx
index 80c16fa..569958f 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -439,7 +439,7 @@
     "                in|out.format= sample format to use with fixed settings\n"
     "                valid values: s8, s16, s32, u8, u16, u32\n"
     "                in|out.voices= number of voices to use\n"
-    "                in|out.buffer-len= length of buffer in microseconds\n"
+    "                in|out.buffer-length= length of buffer in microseconds\n"
     "-audiodev none,id=id,[,prop[=value][,...]]\n"
     "                dummy driver that discards all output\n"
 #ifdef CONFIG_AUDIO_ALSA
@@ -524,7 +524,7 @@
 @item in|out.voices=@var{voices}
 Specify the number of @var{voices} to use.  Default is 1.
 
-@item in|out.buffer=@var{usecs}
+@item in|out.buffer-length=@var{usecs}
 Sets the size of the buffer in microseconds.
 
 @end table