mailmap: update Roman Gushchin's email

I'm moving to a @linux.dev account. Map my old addresses.

Link: https://lkml.kernel.org/r/20220221200006.416377-1-roman.gushchin@linux.dev


Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>