Documentation: cxl: fix typos and improve clarity in memory-devices.rst

Documentation: cxl: fix typos and improve clarity in memory-devices.rst

This patch corrects several typographical issues and improves phrasing
in memory-devices.rst:

- Fixes duplicate word ("1 one") and adjusts phrasing for clarity.
- Adds missing hyphen in "on-device".
- Corrects "a give memory device" to "a given memory device".
- fix singular/plural "decoder resource" -> "decoder resources".
- Clarifies "spans to Host Bridges" -> "spans two Host Bridges".
- change "at a" -> "a"

These changes improve readability and accuracy of the documentation.

Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20250609171130.2375901-1-alok.a.tiwari@oracle.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>