buf[i] can be up to 0xfd, so doubling it and assigning the result to an
unsigned char truncates the value.  Just use an unsigned int instead;
it's only a temporary.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>