lib/int_sqrt: adjust comments

lib/int_sqrt: adjust comments

Our current int_sqrt() is not rough nor any approximation; it calculates
the exact value of: floor(sqrt()).  Document this.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
Cc: Anshul Garg <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: David Miller <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michael Davidson <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>