IB/hfi1: Incorrect sizing of sge for PIO will OOPs

An incorrect sge sizing in the HFI PIO path will cause an OOPs similar to
this:

BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [] hfi1_verbs_send_pio+0x3d8/0x530 [hfi1]
PGD 0
Oops: 0000 1 SMP
 Call Trace:
 ? hfi1_verbs_send_dma+0xad0/0xad0 [hfi1]
 hfi1_verbs_send+0xdf/0x250 [hfi1]
 ? make_rc_ack+0xa80/0xa80 [hfi1]
 hfi1_do_send+0x192/0x430 [hfi1]
 hfi1_do_send_from_rvt+0x10/0x20 [hfi1]
 rvt_post_send+0x369/0x820 [rdmavt]
 ib_uverbs_post_send+0x317/0x570 [ib_uverbs]
 ib_uverbs_write+0x26f/0x420 [ib_uverbs]
 ? security_file_permission+0x21/0xa0
 vfs_write+0xbd/0x1e0
 ? mntput+0x24/0x40
 SyS_write+0x7f/0xe0
 system_call_fastpath+0x16/0x1b

Fix by adding the missing sizing check to correctly determine the sge
length.

Fixes: 77241056 ("IB/hfi1: add driver files")
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>