reset: imx7: delete duplicate case IMX8MP_RESET_PCIEPHY_PERST

Due to commit 2e7fa78d merge conflict, IMX8MP_RESET_PCIEPHY_PERST
has been added, so delete redundant case.

Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>