MAINTAINERS: update Sibi Sankar's email address

MAINTAINERS: update Sibi Sankar's email address

Switch to using oss.qualcomm.com email ID in the MAINTAINERS file.  Also
update mailmap to ensure proper attribution across historical commits.

Link: https://lkml.kernel.org/r/20250926093426.1735334-1-sibi.sankar@oss.qualcomm.com
Signed-off-by: Sibi Sankar <sibi.sankar@oss.qualcomm.com>
Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Carlos Bilbao <carlos.bilbao@kernel.org>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Shannon Nelson <sln@onemain.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>