Fix a scribbler in the PMS driver.

The ESGL bit was left uninitialized when executing the REPORT LUNS
ioctl. This could allow a zeroed data buffer to be treated as a
scatter/gather list. The firmware would eventually walk past the end
of the data buffer, potentially find what looked like a valid
address/length pair, and write the result to semi-random memory.

Obtained from: Dell EMC Isilon
MFC after: 1 week
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D19398