docs: genericirq.rst: don't document chip.c functions twice

Currently, kernel/irq/chip.c is included twice, one for
export functions, and then for internal ones. However, as
the :export:  and :internal: tags are missing, they ended
being included twice.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/core-api/genericirq.rst

@@ -419,6 +419,7 @@ functions which are exported.
 .. kernel-doc:: kernel/irq/manage.c
 
 .. kernel-doc:: kernel/irq/chip.c
+   :export:
 
 Internal Functions Provided
 ===========================
@@ -431,6 +432,7 @@ functions.
 .. kernel-doc:: kernel/irq/handle.c
 
 .. kernel-doc:: kernel/irq/chip.c
+   :internal:
 
 Credits
 =======