ehea: Allocate stats buffer with GFP_KERNEL

Since ehea_get_stats calls ehea_h_query_ehea_port, which
can sleep, we can also sleep when allocating a page in
this function. This fixes some memory allocation failure
warnings seen under low memory conditions.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>