The newly added x550em_a support causes a link failure on ARM because of
an overly long time passed into udelay():

ERROR: "__bad_udelay" [drivers/net/ethernet/intel/ixgbe/ixgbe.ko] undefined!

There are multiple variants of the ixgbe_acquire_swfw_sync_*() function,
and the other ones all use msleep(), so we can safely assume that all
callers are allowed to sleep, which makes msleep() a better replacement
than mdelay().
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 49425dfc ("ixgbe: Add support for x550em_a 10G MAC type")
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>