net: pch_gbe: use readx_poll_timeout_atomic() variant

Use readx_poll_timeout_atomic() instead of open coded variants.

While at it, add __iomem attribute to the parameter of pch_gbe_wait_clr_bit().
This in particular will fix a lot of warnings detected by Sparse, e.g.

.../pch_gbe_main.c:308:26: warning: incorrect type in argument 1 (different address spaces)
.../pch_gbe_main.c:308:26:    expected void const [noderef] __iomem *
.../pch_gbe_main.c:308:26:    got void *reg

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Flavio Suligoi <f.suligoi@asem.it>
Signed-off-by: David S. Miller <davem@davemloft.net>