nvme-pci: avoid hmb desc array idx out-of-bound when hmmaxd set.

hmb descriptor idx out-of-bound occurs in case of below conditions.
preferred = 128MiB
chunk_size = 4MiB
hmmaxd = 1

Current code will not allow rmmod which will free hmb descriptors
to be done successfully in above case.

"descs[i]" will be set in for-loop without seeing any conditions
related to "max_entries" after a single "descs" was allocated by
(max_entries = 1) in this case.

Added a condition into for-loop to check index of descriptors.

Fixes: 044a9df1("nvme-pci: implement the HMB entry number and size limitations")
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>