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-v2012.04.rst b/doc/develop/statistics/u-boot-stats-v2012.04.rst
index f0324d9..1fe67b3 100644
--- a/doc/develop/statistics/u-boot-stats-v2012.04.rst
+++ b/doc/develop/statistics/u-boot-stats-v2012.04.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2012.04
 ======================================
 
-* Processed 773 csets from 126 developers
+* Processed 773 changesets from 126 developers
 
 * 36 employers found