staging: comedi: amplc_pci224: Convert macro GAT_CONFIG to static inline function

Convert macro GAT_CONFIG to static inline function as static inline
functions are preferred over macros. This change is possible since the
arguments at all call sites have the same type.

The uses were updated with Coccinelle:

@r1@
expression dev,reg,chan,src;
@@
-GAT_CONFIG(chan, src)
+pci224_gat_config(chan, src)

Also, the comment describing the macro has been removed.

Signed-off-by: simran singhal <singhalsimran0@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>