IB/hfi1: Fix the size parameter to find_first_bit

The 2nd parameter of 'find_first_bit' is the number of bits to search.
In this case, we are passing 'sizeof(u64)' which is 8.

It is likely that the number of bits of 'port_mask' was expected here.
Use sizeof() * 8 to get the correct number.

It has been spotted by the following coccinelle script:
@@
expression ret, x;

@@
*  ret = \(find_first_bit \| find_first_zero_bit\) (x, sizeof(...));

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Doug Ledford <dledford@redhat.com>