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-v2020.04.rst b/doc/develop/statistics/u-boot-stats-v2020.04.rst
index 6650ad3..c3f839f 100644
--- a/doc/develop/statistics/u-boot-stats-v2020.04.rst
+++ b/doc/develop/statistics/u-boot-stats-v2020.04.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2020.04
 ======================================
 
-* Processed 1639 csets from 189 developers
+* Processed 1639 changesets from 189 developers
 
 * 30 employers found