phy: stm32: fix usbphyc static checker and checkpatch warnings

This patch fixes the following issues:
* warning reported by checkpatch:
WARNING: line over 80 characters
#87: FILE: drivers/phy/st/phy-stm32-usbphyc.c:87:
+static void stm32_usbphyc_get_pll_params(u32 clk_rate, struct pll_params *pll_params)

* bug reported by static checker (Dan Carpenter):
drivers/phy/st/phy-stm32-usbphyc.c:371 stm32_usbphyc_probe()
error: uninitialized symbol 'i'.

* unused stm32_usbphyc structure member: bool pll_enabled.

* unnecessary extra line in stm32_usbphyc_of_xlate

Fixes: 94c358da "phy: stm32: add support for STM32 USB PHY Controller (USBPHYC)"
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>