Documentation: x86: Clarify MBA takes MB as referring to mba_sc

"If the MBA is specified in MB then user can enter the max b/w in MB"
is a tautology. How can the user know if the schemata takes a percentage
or a MB/s value?

This is referring to whether the software controller is interpreting
the schemata's value. Make this clear.
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/x86/resctrl_ui.rst

@@ -677,8 +677,8 @@ allocations can overlap or not. The allocations specifies the maximum
 b/w that the group may be able to use and the system admin can configure
 the b/w accordingly.
 
-If the MBA is specified in MB(megabytes) then user can enter the max b/w in MB
-rather than the percentage values.
+If resctrl is using the software controller (mba_sc) then user can enter the
+max b/w in MB rather than the percentage values.
 ::
 
   # echo "L3:0=3;1=c\nMB:0=1024;1=500" > /sys/fs/resctrl/p0/schemata