misc: Spelling and grammar fixes in comments

* it's -> its
* grammar fix in ui/vnc-enc-zywrle.h

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Don Koch <dkoch@verizon.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff --git a/qapi-schema.json b/qapi-schema.json
index 60f3fd1..a003aa1 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1914,7 +1914,7 @@
 #
 # Since: 0.14.0
 #
-# Notes: This command only exists as a stop-gap.  It's use is highly
+# Notes: This command only exists as a stop-gap.  Its use is highly
 #        discouraged.  The semantics of this command are not guaranteed.
 #
 #        Known limitations:
diff --git a/slirp/if.c b/slirp/if.c
index 87ca8a5..fb7acf8 100644
--- a/slirp/if.c
+++ b/slirp/if.c
@@ -142,7 +142,7 @@
 
 /*
  * Send a packet
- * We choose a packet based on it's position in the output queues;
+ * We choose a packet based on its position in the output queues;
  * If there are packets on the fastq, they are sent FIFO, before
  * everything else.  Otherwise we choose the first packet from the
  * batchq and send it.  the next packet chosen will be from the session
diff --git a/ui/vnc-enc-zywrle.h b/ui/vnc-enc-zywrle.h
index 1ff40b1..d436d58 100644
--- a/ui/vnc-enc-zywrle.h
+++ b/ui/vnc-enc-zywrle.h
@@ -305,7 +305,7 @@
    |L1H0H1H0|L1H0H1H0|L1H0H1H0|L1H0H1H0| : level 1
 
  In this method, H/L and X0/X1 is always same position.
- This lead us to more speed and less memory.
+ This leads us to more speed and less memory.
  Of cause, the result of both method is quite same
  because it's only difference that coefficient position.
 */