igc: field prep conversion

Refactor igc driver to use FIELD_PREP(), which reduces lines of code
and adds clarity of intent.

This code was generated by the following coccinelle/spatch script and
then manually repaired in a later patch.

@prep2@
constant shift,mask;
type T;
expression a;
@@
-(((T)(a) << shift) & mask)
+FIELD_PREP(mask, a)

@prep@
constant shift,mask;
type T;
expression a;
@@
-((T)((a) << shift) & mask)
+FIELD_PREP(mask, a)

Cc: Julia Lawall <Julia.Lawall@inria.fr>
Cc: Sasha Neftin <sasha.neftin@intel.com>
Reviewed-by: Marcin Szycik <marcin.szycik@linux.intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>