usb: host: xhci-plat: fix possible kernel oops while resuming

If this driver enables the xHC clocks while resuming from sleep, it calls
clk_prepare_enable() without checking for errors and blithely goes on to
read/write the xHC's registers -- which, with the xHC not being clocked,
at least on ARM32 usually causes an imprecise external abort exceptions
which cause kernel oops.  Currently, the chips for which the driver does
the clock dance on suspend/resume seem to be the Broadcom STB SoCs, based
on ARM32 CPUs, as it seems...

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Fixes: 8bd954c5

 ("usb: host: xhci-plat: suspend and resume clocks")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20231019102924.2797346-19-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>