Documentation/DMA-API-HOWTO.txt: minor grammar corrections

that the mapping code will work correctly on all dma implementations without

any dependency on the specifics of the underlying implementation. Using the

returned address without checking for errors could result in failures ranging

from panics to silent data corruption. Couple of example of incorrect ways to

check for errors that make assumptions about the underlying dma implementation

are as follows and these are applicable to dma_map_page() as well.

from panics to silent data corruption. A couple of examples of incorrect ways

to check for errors that make assumptions about the underlying dma

implementation are as follows and these are applicable to dma_map_page() as

well.

Incorrect example 1:

	dma_addr_t dma_handle;