doc: mpsc: Add missed 'end'

Adds missed 'end' in the 'Internals' chapter.

(cherry picked from commit 2e97e5d)

Original-Signed-off-by: Andrej Butok <andrey.butok@nxp.com>
GitOrigin-RevId: 2e97e5d
Change-Id: Ifc7d1462e010dcf986101c2508c4d95982a8fc00
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5032796
Reviewed-by: Keith Short <keithshort@chromium.org>
Commit-Queue: Keith Short <keithshort@chromium.org>
Tested-by: Keith Short <keithshort@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>

doc/kernel/data_structures/mpsc_pbuf.rst

@@ -54,7 +54,7 @@ Header state:
 +-------+------+----------------------+
 
 Packet buffer space contains free space, valid user packets and internal skip
-packets. Internal skip packets indicates padding, e.g. at the of the buffer.
+packets. Internal skip packets indicates padding, e.g. at the end of the buffer.
 
 Allocation
 ^^^^^^^^^^