soc: mediatek: mutex: Simplify with devm_platform_get_and_ioremap_resource()

soc: mediatek: mutex: Simplify with devm_platform_get_and_ioremap_resource()

Convert platform_get_resource(), devm_ioremap_resource() to a single
call to devm_platform_get_and_ioremap_resource(), as this is exactly
what this function does.

While at it, also remove a redundant call to of_address_to_resource(),
as this was getting the address of the same resource index 0: we can
as well get the iostart from the 'regs' pointer.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220623121701.107512-1-angelogioacchino.delregno@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>