MAINTAINERS: add git tree for random.c

This is handy not just for humans, but also so that the 0-day bot can
automatically test posted mailing list patches against the right tree.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

Author: zx2c4

MAINTAINERS

@@ -15989,6 +15989,7 @@ F:	arch/mips/generic/board-ranchu.c
 RANDOM NUMBER DRIVER
 M:	"Theodore Ts'o" <tytso@mit.edu>
 M:	Jason A. Donenfeld <Jason@zx2c4.com>
+T:	git https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git
 S:	Maintained
 F:	drivers/char/random.c