phy: freescale: imx8m-pcie: Add one missing error return

There should be one error return when fail to fetch the perst reset.
Add the missing error return.

Fixes: dce9edff

 ("phy: freescale: imx8m-pcie: Add i.MX8MP PCIe PHY support")

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/1671433941-2037-1-git-send-email-hongxing.zhu@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>