The assignment to nbytes is redundant, the while loop needs
to just refer to the value in walk.nbytes and the value of
nbytes is being re-assigned inside the loop on both paths
of the following if-statement.  Remove redundant assignment.

Cleans up clang scan build warning:
warning: Although the value stored to 'nbytes' is used in
the enclosing expression, the value is never actually read
from 'nbytes' [deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>