MAINTAINERS: fix DWMAC S32 entry

Using L: with more than a bare email address causes getmaintainer.pl
to be unable to parse the entry. Fix this by doing as other entries
that use this email address and convert it to an R: entry.

Link: https://patch.msgid.link/20250221005012.1051897-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>