doc: Use "changesets" not "csets" in statistics pages

To make things more human readable, say "changesets from" rather than
"csets from" in all our historical pages here. Moving forward this has
been changed in our gitdm with b034e399e31a ("gitdm: fix typo csets").

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/doc/develop/statistics/u-boot-stats-v2017.05.rst b/doc/develop/statistics/u-boot-stats-v2017.05.rst
index bae4788..39e7684 100644
--- a/doc/develop/statistics/u-boot-stats-v2017.05.rst
+++ b/doc/develop/statistics/u-boot-stats-v2017.05.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2017.05
 ======================================
 
-* Processed 915 csets from 139 developers
+* Processed 915 changesets from 139 developers
 
 * 29 employers found