Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index 14e0f93..00ecf62 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -241,7 +241,7 @@
 
 	args->cbl_layout_type = ntohl(*p++);
 	/* Depite the spec's xdr, iomode really belongs in the FILE switch,
-	 * as it is unuseable and ignored with the other types.
+	 * as it is unusable and ignored with the other types.
 	 */
 	iomode = ntohl(*p++);
 	args->cbl_layoutchanged = ntohl(*p++);
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 3ac5bd6..2f093ed 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -301,7 +301,7 @@
  * disk, but it retrieves and clears ctx->error after synching, despite
  * the two being set at the same time in nfs_context_set_write_error().
  * This is because the former is used to notify the _next_ call to
- * nfs_file_write() that a write error occured, and hence cause it to
+ * nfs_file_write() that a write error occurred, and hence cause it to
  * fall back to doing a synchronous write.
  */
 static int
diff --git a/fs/nfs/nfs4filelayout.h b/fs/nfs/nfs4filelayout.h
index 085a354..7c44579 100644
--- a/fs/nfs/nfs4filelayout.h
+++ b/fs/nfs/nfs4filelayout.h
@@ -33,7 +33,7 @@
 #include "pnfs.h"
 
 /*
- * Field testing shows we need to support upto 4096 stripe indices.
+ * Field testing shows we need to support up to 4096 stripe indices.
  * We store each index as a u8 (u32 on the wire) to keep the memory footprint
  * reasonable. This in turn means we support a maximum of 256
  * RFC 5661 multipath_list4 structures.