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-v2018.05.rst b/doc/develop/statistics/u-boot-stats-v2018.05.rst
index 57a3d83..648832a 100644
--- a/doc/develop/statistics/u-boot-stats-v2018.05.rst
+++ b/doc/develop/statistics/u-boot-stats-v2018.05.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2018.05
 ======================================
 
-* Processed 977 csets from 128 developers
+* Processed 977 changesets from 128 developers
 
 * 26 employers found