drivers: ufs: ufs-mediatek: fix phy handling

drivers: ufs: ufs-mediatek: fix phy handling

Currently mphy is declared as a pointer inside ufs_mtk_host struct, but
it is never initialized.

Fix this by using a struct phy directly in ufs_mtk_host struct instead
of a struct phy*. Update all call to mphy accordingly.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Link: https://patch.msgid.link/20260318-mt8195-add-ufs-support-v2-6-f18eeeeb0e72@baylibre.com
Signed-off-by: David Lechner <dlechner@baylibre.com>