usb: dwc3: core: Fix compile warning on s390 gcc in dwc3_get_phy call

Recent commit introduced support for reading Multiport PHYs and
while doing so iterated over an integer variable which runs from
[0-254] in the worst case scenario. But S390 compiler treats it as a
warning and complains that the integer write to string can go to 11
characters. Fix this by modifying iterator variable to u8.

Suggested-by: Johan Hovold <johan@kernel.org>
Fixes: 30a46746 ("usb: dwc3: core: Refactor PHY logic to support Multiport Controller")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202404241215.Mib19Cu7-lkp@intel.com/


Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20240426050512.57384-1-quic_kriskura@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>