ice: cleanup language in ice.rst for fw.app

The documentation for the ice driver around "fw.app" has a spelling
mistake in variation. Additionally, the language of "shall have a unique
name" sounds like a requirement. Reword this to read more like
a description or property.

Reported-by: Benjamin Fisher <benjamin.l.fisher@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>