Documentation: admin-guide: correct "it's" to possessive "its"

Correct 2 uses of "it's" to the possessive "its" as needed.

Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Darrick J. Wong <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Jonathan Corbet <[e-mail]>
Reviewed-by: Darrick J. Wong <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/admin-guide/mm/numa_memory_policy.rst

···
 	* A task may install a new VMA policy on a sub-range of a
 	  previously mmap()ed region.  When this happens, Linux splits
 	  the existing virtual memory area into 2 or 3 VMAs, each with
-	  it's own policy.
+	  its own policy.
 
 	* By default, VMA policy applies only to pages allocated after
 	  the policy is installed.  Any pages already faulted into the

Documentation/admin-guide/xfs.rst

···
 	are any integer multiple of a valid ``sunit`` value.
 
 	Typically the only time these mount options are necessary if
-	after an underlying RAID device has had it's geometry
+	after an underlying RAID device has had its geometry
 	modified, such as adding a new disk to a RAID5 lun and
 	reshaping it.