mux: mmio: fix regmap leak on probe failure

mux: mmio: fix regmap leak on probe failure

The mmio regmap that may be allocated during probe is never freed.

Switch to using the device managed allocator so that the regmap is
released on probe failures (e.g. probe deferral) and on driver unbind.

Fixes: 61de83fd8256 ("mux: mmio: Do not use syscon helper to build regmap")
Cc: stable@vger.kernel.org	# 6.16
Cc: Andrew Davis <afd@ti.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Andrew Davis <afd@ti.com>
Link: https://patch.msgid.link/20251127134702.1915-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>