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-v2018.01.rst b/doc/develop/statistics/u-boot-stats-v2018.01.rst
index b2b3d0f..a5c68e7 100644
--- a/doc/develop/statistics/u-boot-stats-v2018.01.rst
+++ b/doc/develop/statistics/u-boot-stats-v2018.01.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2018.01
 ======================================
 
-* Processed 785 csets from 132 developers
+* Processed 785 changesets from 132 developers
 
 * 32 employers found