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-v2015.07.rst b/doc/develop/statistics/u-boot-stats-v2015.07.rst
index 7999b27..ed6baee 100644
--- a/doc/develop/statistics/u-boot-stats-v2015.07.rst
+++ b/doc/develop/statistics/u-boot-stats-v2015.07.rst
@@ -3,7 +3,7 @@
 Release Statistics for U-Boot v2015.07
 ======================================
 
-* Processed 1563 csets from 156 developers
+* Processed 1563 changesets from 156 developers
 
 * 28 employers found