dma-buf: update exp_name when using dma_buf_export()

commit c0b00a52 ("dma-buf: update debugfs output") modified the
default exporter name to be the KBUILD_MODNAME pre-processor
macro instead of __FILE__ but the documentation was not updated.

Also the "Supporting existing mmap interfaces in exporters" section
title seems wrong since talks about the interface used by importers.
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/dma-buf-sharing.txt

@@ -66,7 +66,7 @@ The dma_buf buffer sharing API usage contains the following steps:
 
    Exporting modules which do not wish to provide any specific name may use the
    helper define 'dma_buf_export()', with the same arguments as above, but
-   without the last argument; a __FILE__ pre-processor directive will be
+   without the last argument; a KBUILD_MODNAME pre-processor directive will be
    inserted in place of 'exp_name' instead.
 
 2. Userspace gets a handle to pass around to potential buffer-users
@@ -352,7 +352,7 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
 
    No special interfaces, userspace simply calls mmap on the dma-buf fd.
 
-2. Supporting existing mmap interfaces in exporters
+2. Supporting existing mmap interfaces in importers
 
    Similar to the motivation for kernel cpu access it is again important that
    the userspace code of a given importing subsystem can use the same interfaces