linux/pagemap.h: Fixed a typo in a code comment.

Corrected a minor typo in a code comment where 'be' was missing.
Signed-off-by: NRaymond L. Rivera <ray.l.rivera@gmail.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

include/linux/pagemap.h

@@ -96,7 +96,7 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
 }
 
 /*
- * The page cache can done in larger chunks than
+ * The page cache can be done in larger chunks than
  * one page, because it allows for more efficient
  * throughput (it can then be mapped into user
  * space in smaller chunks for same flexibility).