MAINTAINERS: update the 'T:' entry for xtensa

All development activity for xtensa architecture have been routed
through the github.com/jcmvbkbc/linux-xtensa tree for the last few
years. Update the 'T:' entry in the MAINTAINERS file to reflect that.

Github deprecated the git:// links about a year ago, so let's move to
the https:// URLs instead.
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://github.blog/2021-09-01-improving-git-protocol-security-github/Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

MAINTAINERS

@@ -20097,7 +20097,7 @@ M:	Chris Zankel <chris@zankel.net>
 M:	Max Filippov <jcmvbkbc@gmail.com>
 L:	linux-xtensa@linux-xtensa.org
 S:	Maintained
-T:	git git://github.com/czankel/xtensa-linux.git
+T:	git https://github.com/jcmvbkbc/linux-xtensa.git
 F:	arch/xtensa/
 F:	drivers/irqchip/irq-xtensa-*