doc: spelling error changes

Fixed multiple spelling errors.

Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Carlos E. Garcia <carlos@cgarcia.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/DMA-attributes.txt

@@ -98,5 +98,5 @@ DMA_ATTR_FORCE_CONTIGUOUS
 By default DMA-mapping subsystem is allowed to assemble the buffer
 allocated by dma_alloc_attrs() function from individual pages if it can
 be mapped as contiguous chunk into device dma address space. By
-specifing this attribute the allocated buffer is forced to be contiguous
+specifying this attribute the allocated buffer is forced to be contiguous
 also in physical memory.