IB/ipath: Fix module parameter description for disable_sma

Describe disable_sma parameter with its name rather than the internal
ib_ipath_disable_sma variable name, so that the description shows up
properly in modinfo.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>