NVMe: Use last bytes of f/w rev SCSI Inquiry

After skipping right-padded spaces, use the last four bytes of the
firmware revision when reporting the Inquiry Product Revision. These
are generally more indicative to what is running.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Acked-by: Vishal Verma <vishal.l.verma@linux.intel.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>