MAINTAINERS: power: supply: max17040: add entry with reviewers

The Maxim max17040 fuel gauge driver supports several devices used on
multiple different boards.  The driver is incomplete and has few known
issues.  Fixing these might break other platforms so mention recent
contributors who can provide feedback.  This way most of interested
parties might help reviewing the patches.

Cc: Iskren Chernev <iskren.chernev@gmail.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Matheus Castello <matheus@castello.eng.br>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>