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-v2017.03.rst b/doc/develop/statistics/u-boot-stats-v2017.03.rst
index 733c975..bce2fe1 100644
--- a/doc/develop/statistics/u-boot-stats-v2017.03.rst
+++ b/doc/develop/statistics/u-boot-stats-v2017.03.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2017.03
 ======================================
 
-* Processed 664 csets from 126 developers
+* Processed 664 changesets from 126 developers
 
 * 29 employers found