Maintainers.txt: update email address for Leif Lindholm

Leif now works at NUVIA Inc, update email address accordingly.

Cc: Andy Hayes <andy.hayes@displaylink.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Marcin Wojtas <mw@semihalf.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Pete Batard <pete@akeo.ie>
Cc: Leif Lindholm <leif@nuviainc.com>
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>