lib: radix-tree: delete duplicated words

Drop the repeated word "be".

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200823040508.26086-1-rdunlap@infradead.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>