mailmap: update Seth Forshee's email address

seth.forshee@canonical.com is no longer valid, use sforshee@kernel.org
instead.

Link: https://lkml.kernel.org/r/20220628200734.424495-1-sforshee@kernel.orgSigned-off-by: NSeth Forshee <sforshee@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>

.mailmap

@@ -368,6 +368,7 @@ Sean Nyekjaer <sean@geanix.com> <sean.nyekjaer@prevas.dk>
 Sebastian Reichel <sre@kernel.org> <sebastian.reichel@collabora.co.uk>
 Sebastian Reichel <sre@kernel.org> <sre@debian.org>
 Sedat Dilek <sedat.dilek@gmail.com> <sedat.dilek@credativ.de>
+Seth Forshee <sforshee@kernel.org> <seth.forshee@canonical.com>
 Shiraz Hashim <shiraz.linux.kernel@gmail.com> <shiraz.hashim@st.com>
 Shuah Khan <shuah@kernel.org> <shuahkhan@gmail.com>
 Shuah Khan <shuah@kernel.org> <shuah.khan@hp.com>