docs: pstore-blk.rst: fix kernel-doc tags

There is currently a problem with kernel-doc tags from blk.c:

	.../Documentation/admin-guide/pstore-blk:239: ./fs/pstore/blk.c:175: WARNING: Duplicate C declaration, also defined in 'admin-guide/pstore-blk'.
	Declaration is 'register_pstore_device'.
	.../Documentation/admin-guide/pstore-blk:239: ./fs/pstore/blk.c:432: WARNING: Duplicate C declaration, also defined in 'admin-guide/pstore-blk'.
	Declaration is 'register_pstore_blk'.
	.../Documentation/admin-guide/pstore-blk:242: ./include/linux/pstore_blk.h:43: WARNING: Duplicate C declaration, also defined in 'admin-guide/pstore-blk'.
	Declaration is 'pstore_device_info'.

Basically, the internal parts is shown with :export:, instead
of :internal:. Yet, there are some other exported docs that
aren't at the document, because they lack :identifiers:.

So, instead, let's just use :export: at the kAPI part of
the documentation.

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/admin-guide/pstore-blk.rst

@@ -154,17 +154,11 @@ Configurations for driver
 Only a block device driver cares about these configurations. A block device
 driver uses ``register_pstore_blk`` to register to pstore/blk.
 
-.. kernel-doc:: fs/pstore/blk.c
-   :identifiers: register_pstore_blk
-
 A non-block device driver uses ``register_pstore_device`` with
 ``struct pstore_device_info`` to register to pstore/blk.
 
 .. kernel-doc:: fs/pstore/blk.c
-   :identifiers: register_pstore_device
-
-.. kernel-doc:: include/linux/pstore_blk.h
-   :identifiers: pstore_device_info
+   :export:
 
 Compression and header
 ----------------------
@@ -237,7 +231,7 @@ For developer reference, here are all the important structures and APIs:
    :internal:
 
 .. kernel-doc:: fs/pstore/blk.c
-   :export:
+   :internal:
 
 .. kernel-doc:: include/linux/pstore_blk.h
    :internal: