mlx4_core: Fix max_eqs masking in QUERY_DEV_CAP

log_max_eqs is a 4-bit field, not a 3-bit field in the response to the
QUERY_DEV_CAP FW command, so we should mask with 0xf instead of 0x7
when reading it.

Found by Yossi Leybovitch of Mellanox.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>