bnxt_en: fix ternary sign extension bug in bnxt_show_temp()

The problem is that bnxt_show_temp() returns long but "rc" is an int
and "len" is a u32.  With ternary operations the type promotion is quite
tricky.  The negative "rc" is first promoted to u32 and then to long so
it ends up being a high positive value instead of a a negative as we
intended.

Fix this by removing the ternary.

Fixes: d69753fa ("bnxt_en: return proper error codes in bnxt_show_temp")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>